Controlling transitions in optically switchable devices

ABSTRACT

The embodiments herein relate to methods for controlling an optical transition in an optically switchable device, and optically switchable devices configured to perform such methods. In various embodiments, non-optical (e.g., electrical) feedback is used to help control an optical transition. The feedback may be used for a number of different purposes. In many implementations, the feedback is used to control an ongoing optical transition.

CROSS REFERENCE TO RELATED APPLICATIONS

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in its entirety and for all purposes.

BACKGROUND

Electrochromic (EC) devices are typically multilayer stacks including(a) at least one layer of electrochromic material, that changes itsoptical properties in response to the application of an electricalpotential, (b) an ion conductor (IC) layer that allows ions, such aslithium ions, to move through it, into and out from the electrochromicmaterial to cause the optical property change, while preventingelectrical shorting, and (c) transparent conductor layers, such astransparent conducting oxides or TCOs, over which an electricalpotential is applied to the electrochromic layer. In some cases, theelectric potential is applied from opposing edges of an electrochromicdevice and across the viewable area of the device. The transparentconductor layers are designed to have relatively high electronicconductances. Electrochromic devices may have more than theabove-described layers such as ion storage or counter electrode layersthat optionally change optical states.

Due to the physics of the device operation, proper function of theelectrochromic device depends upon many factors such as ion movementthrough the material layers, the electrical potential required to movethe ions, the sheet resistance of the transparent conductor layers, andother factors. The size of the electrochromic device plays an importantrole in the transition of the device from a starting optical state to anending optical state (e.g., from tinted to clear or clear to tinted).The conditions applied to drive such transitions can have quitedifferent requirements for different sized devices or differentoperating conditions.

What are needed are improved methods for driving optical transitions inelectrochromic devices.

SUMMARY

Various embodiments herein relate to methods for transitioning anoptically switchable device using feedback obtained during thetransition to control the ongoing transition. Certain embodiments relateto optically switchable devices having controllers with instructions totransition the optically switchable device using feedback obtainedduring the transition. Further, in some embodiments, groups of opticallyswitchable devices are controlled together based on electrical feedbackobtained during the transition. The optically switchable devices can beprobed by applying certain electrical conditions (e.g., voltage pulsesand/or current pulses) to the optically switchable devices. Anelectrical response to the probing can be used as feedback to controlthe ongoing transition.

In one aspect of the disclosed embodiments, a method of controlling anoptical transition of an optically switchable device from a startingoptical state to an ending optical state is provided, the methodincluding: (a) applying a voltage or current for driving the opticallyswitchable device to transition from the starting optical state to theending optical state, where the applied voltage or current is applied tobus bars of the optically switchable device; (b) before the transitionis complete, determining an electrical characteristic of the opticallyswitchable device; and (c) using the determined electricalcharacteristic as feedback to adjust the applied voltage or current tofurther control the optically switchable device transition.

In a number of embodiments, the optically switchable device is anelectrochromic (EC) window. Operation (c) may include substantiallymatching, during the transition, the tint level of the EC window to thetint level of a second EC window proximate the EC window. This allowsmore than one window to be controlled to matching tint levels.

Different types of feedback may be used. In some embodiments, thedetermined electrical characteristic includes an open circuit voltageacross two electrodes of the optically switchable device. In these orother cases, the determined electrical characteristic may include acurrent flowing between two electrodes of the optically switchabledevice. In some examples, the determined electrical characteristicincludes at least one of a voltage and a current, where operation (c)includes adjusting an applied current or voltage used to drive thetransition based on the determined electrical characteristic to ensurethat the optically switchable device is maintained within a safeoperating current range and/or within a safe operating voltage rangeduring the optical transition. The safe operating current range may havea maximum magnitude between about 70-250 μA/cm². The safe operatingvoltage range may have a maximum magnitude between about 5-9V.

In certain embodiments, the determined electrical characteristicincludes at least one of a voltage and a current, and (c) includesadjusting an applied current or voltage used to drive the transitionbased on the determined electrical characteristic to ensure that theoptical transition is occurring at a rate of transition that is at leastas high as a target rate of transition. In some cases, (c) includesadjusting the applied current or voltage based on the determinedelectrical characteristic to ensure that the optical transition occurswithin a target timeframe. In these or other cases, the determinedelectrical characteristic may include at least one of a voltage and acurrent, and (c) includes adjusting an applied current or voltage usedto drive the transition based on the determined electricalcharacteristic to determine whether the optically switchable device isat or near the ending optical state. Further, in some cases thedetermined electrical characteristic includes a current that occurs inresponse to open circuit voltage conditions applied to the opticallyswitchable device.

In some cases, the method further includes determining a quantity ofcharge delivered to drive the optical transition, and based on thedetermined quantity of charge delivered, determining whether theoptically switchable device is at or near the ending optical state. Themethod may also include receiving a command to transition the opticallyswitchable device to a third optical state after initiation of theoptical transition from the starting optical state to the ending opticalstate, where the third optical state is different from the endingoptical state, where (c) includes adjusting an applied current orvoltage used to drive the optical transition based on the determinedelectrical characteristic to thereby drive the optically switchabledevice to the third optical state.

In another aspect of the disclosed embodiments, a method of maintainingsubstantially matching tint levels or tint rates in a plurality ofelectrochromic (EC) windows is provided, the method including: (a)probing the plurality of EC windows to determine an electrical responsefor each window; (b) comparing the determined electrical responses forthe plurality of EC windows; and (c) scaling a voltage or currentapplied to each of the plurality of EC windows to thereby match the tintlevels or tint rates in each of the plurality of EC windows.

In a further aspect of the disclosed embodiments, a method oftransitioning a plurality of electrochromic (EC) windows atsubstantially matching tint rates is provided, the method including: (a)determining a transition time over which the plurality of EC windows areto be transitioned from a starting optical state to an ending opticalstate, where the transition time is based, at least in part, on aminimum time over which a slowest transitioning window in the pluralityof EC windows transitions from the starting optical state to the endingoptical state; (b) applying one or more drive conditions to each of thewindows in the plurality of windows, where the one or more driveconditions applied to each window are sufficient to cause each window totransition from the starting optical state to the ending optical statesubstantially within the transition time.

In certain implementations, the method further includes: while applyingthe one or more drive conditions, probing the plurality of EC windows todetermine an electrical response for each window, measuring theelectrical response for each window, determining whether the electricalresponse for each window indicates that the window will reach the endingoptical state within the transition time, and if it is determined thatthe window will reach the ending optical state within the transitiontime, continuing to apply the driving conditions to reach the endingoptical state, and if it is determined that the window will not reachthe ending optical state within the transition time, increasing avoltage and/or current applied to the window to thereby cause the windowto reach the ending optical state within the transition time.

The method may further include when determining whether the electricalresponse for each window indicates that the window will reach the endingstate within the transition time, if it is determined that the windowwill reach the ending optical state substantially before the transitiontime, decreasing a drive voltage and/or current applied to the window tothereby cause the window to reach the ending optical state at a timecloser to the transition time than would otherwise occur withoutdecreasing the drive voltage and/or current. The transition time may bebased on a number of factors. For instance, in some cases the transitiontime is based, at least in part, on a size of a largest window in theplurality of EC windows. This can help ensure that the windows can alltransition at the same rate.

The plurality of EC windows may be specifically defined in some cases.For instance, the method may include defining the plurality of ECwindows to be transitioned based on one or more criteria selected fromthe group consisting of: pre-defined zones of windows,instantaneously-defined zones of windows, window properties, and userpreferences. A number of different sets of windows can be defined, andthe sets of windows can be re-defined on-the-fly in some embodiments.For example, defining the plurality of EC windows to be transitioned mayinclude determining a first plurality of EC windows and determining asecond plurality of EC windows, where the transition time determined in(a) is a first transition time over which the first plurality of ECwindows are to be transitioned, and where the transition time in (b) isthe first transition time, and further including: (c) after beginning toapply the one or more drive conditions in (b) and before the firstplurality of EC windows reaches the ending optical state, determining asecond transition time over which the second plurality of EC windows areto be transitioned to a third optical state, where the third opticalstate may be the starting optical state, the ending optical state, or adifferent optical state, where the second transition time is based, atleast in part, on a minimum time over which a slowest transitioningwindow in the second plurality of EC windows transitions to the thirdoptical state, and (d) applying one or more drive conditions to each ofthe windows in the second plurality of EC windows, where the one or moredrive conditions applied to each window are sufficient to cause eachwindow to transition to the third optical state substantially within thesecond transition time. In some embodiments, each window in theplurality of EC windows includes a memory component including aspecified transition time for that window, where (a) includes comparingthe specified transition time for each window in the plurality of ECwindows to thereby determine which window is the slowest transitioningwindow in the plurality of EC windows.

These and other features will be described in further detail below withreference to the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates current and voltage profiles during an opticaltransition using a simple voltage control algorithm.

FIG. 2 depicts a family of charge (Q) vs. temperature (T) curves forparticular voltages.

FIGS. 3A and 3B show current and voltage profiles resulting from aspecific control method in accordance with certain embodiments.

FIG. 3C shows a flow chart depicting control of current during aninitial stage of an optical transition.

FIG. 4A schematically depicts a planar bus bar arrangement according tocertain embodiments.

FIG. 4B presents a simplified plot of the local voltage value on eachtransparent conductive layer as a function of position on the layer.

FIG. 4C is a simplified plot of V_(eff) as a function of position acrossthe device.

FIG. 5 is a graph depicting certain voltage and current profilesassociated with driving an electrochromic device from clear to tinted.

FIG. 6A is a graph depicting an optical transition in which a drop inapplied voltage from V_(drive) to V_(hold) results in a net current flowestablishing that the optical transition has proceeded far enough topermit the applied voltage to remain at V_(hold) for the duration of theending optical state.

FIG. 6B is a graph depicting an optical transition in which an initialdrop in applied voltage from V_(drive) to V_(hold) results in a netcurrent flow indicating that the optical transition has not yetproceeded far enough to permit the applied voltage to remain at V_(hold)for the duration of the ending optical state.

FIGS. 7A-7D are flow charts illustrating various methods for controllingan optical transition in an optically switchable device using electricalfeedback.

FIGS. 8A and 8B show graphs depicting the total charge delivered overtime and the voltage applied over time during an electrochromictransition when using the method of FIG. 7D to probe and monitor theprogress of the transition.

FIG. 8C illustrates an electrochromic window having a pair of voltagesensors on the transparent conductive oxide layers according to anembodiment.

FIGS. 9A and 9B are flow charts depicting further methods forcontrolling an optical transition in an optically switchable deviceusing electrical feedback.

FIGS. 9C and 9D present flow charts for methods of controlling multiplewindows simultaneously to achieve matching tint levels or tint rates.

FIG. 10 depicts a curtain wall having a number of electrochromicwindows.

FIG. 11 is a schematic illustration of a controller that may be used tocontrol an optically switchable device according to the methodsdescribed herein.

FIG. 12 depicts a cross-sectional view of an IGU according to anembodiment.

FIG. 13 illustrates a window controller and associated components.

FIG. 14 is a schematic depiction of an electrochromic device incross-section.

FIG. 15 is a schematic cross-section of an electrochromic device in aclear state (or transitioning to a clear state).

FIG. 16 is a schematic cross-section of an electrochromic device in atinted state (or transitioning to a tinted state).

FIG. 17 is a schematic cross-section of an electrochromic device in atinted state, where the device has an interfacial region that does notcontain a distinct ion conductor layer.

DETAILED DESCRIPTION Definitions

An “optically switchable device” is a thin device that changes opticalstate in response to electrical input. It reversibly cycles between twoor more optical states. Switching between these states is controlled byapplying predefined current and/or voltage to the device. The devicetypically includes two thin conductive sheets that straddle at least oneoptically active layer. The electrical input driving the change inoptical state is applied to the thin conductive sheets. In certainimplementations, the input is provided by bus bars in electricalcommunication with the conductive sheets.

While the disclosure emphasizes electrochromic devices as examples ofoptically switchable devices, the disclosure is not so limited. Examplesof other types of optically switchable device include certainelectrophoretic devices, liquid crystal devices, and the like. Opticallyswitchable devices may be provided on various optically switchableproducts, such as optically switchable windows. However, the embodimentsdisclosed herein are not limited to switchable windows. Examples ofother types of optically switchable products include mirrors, displays,and the like. In the context of this disclosure, these products aretypically provided in a non-pixelated format.

An “optical transition” is a change in any one or more opticalproperties of an optically switchable device. The optical property thatchanges may be, for example, tint, reflectivity, refractive index,color, etc. In certain embodiments, the optical transition will have adefined starting optical state and a defined ending optical state. Forexample the starting optical state may be 80% transmissivity and theending optical state may be 50% transmissivity. The optical transitionis typically driven by applying an appropriate electric potential acrossthe two thin conductive sheets of the optically switchable device.

A “starting optical state” is the optical state of an opticallyswitchable device immediately prior to the beginning of an opticaltransition. The starting optical state is typically defined as themagnitude of an optical state which may be tint, reflectivity,refractive index, color, etc. The starting optical state may be amaximum or minimum optical state for the optically switchable device;e.g., 90% or 4% transmissivity in some cases. In certain cases a minimumtransmissivity may be about 2% or lower, for example about 1% or lower.Alternatively, the starting optical state may be an intermediate opticalstate having a value somewhere between the maximum and minimum opticalstates for the optically switchable device; e.g., 50% transmissivity.

An “ending optical state” is the optical state of an opticallyswitchable device immediately after the complete optical transition froma starting optical state. The complete transition occurs when opticalstate changes in a manner understood to be complete for a particularapplication. For example, a complete tinting might be deemed atransition from 75% optical transmissivity to 10% transmissivity. Theending optical state may be a maximum or minimum optical state for theoptically switchable device; e.g., 90% or 4% transmissivity. In certaincases a minimum transmissivity may be about 2% or lower, for exampleabout 1% or lower. Alternatively, the ending optical state may be anintermediate optical state having a value somewhere between the maximumand minimum optical states for the optically switchable device; e.g.,50% transmissivity.

“Bus bar” refers to an electrically conductive strip attached to aconductive layer such as a transparent conductive electrode spanning thearea of an optically switchable device. The bus bar delivers electricalpotential and current from an external lead to the conductive layer. Anoptically switchable device includes two or more bus bars, eachconnected to a single conductive layer of the device. In variousembodiments, a bus bar forms a long thin line that spans most of thelength of the length or width of a device. Often, a bus bar is locatednear the edge of the device.

“Applied Voltage” or V_(app) refers the difference in potential appliedto two bus bars of opposite polarity on the electrochromic device. Eachbus bar is electronically connected to a separate transparent conductivelayer. The applied voltage may have different magnitudes or functionssuch as driving an optical transition or holding an optical state.Between the transparent conductive layers are sandwiched the opticallyswitchable device materials such as electrochromic materials. Each ofthe transparent conductive layers experiences a potential drop betweenthe position where a bus bar is connected to it and a location remotefrom the bus bar. Generally, the greater the distance from the bus bar,the greater the potential drop in a transparent conducting layer. Thelocal potential of the transparent conductive layers is often referredto herein as the V_(TCL). Bus bars of opposite polarity may be laterallyseparated from one another across the face of an optically switchabledevice.

“Effective Voltage” or V_(eff) refers to the potential between thepositive and negative transparent conducting layers at any particularlocation on the optically switchable device. In Cartesian space, theeffective voltage is defined for a particular x,y coordinate on thedevice. At the point where V_(eff) is measured, the two transparentconducting layers are separated in the z-direction (by the devicematerials), but share the same x,y coordinate.

“Hold Voltage” refers to the applied voltage necessary to indefinitelymaintain the device in an ending optical state. In some cases, withoutapplication of a hold voltage, electrochromic windows return to theirnatural tint state. In other words, maintenance of a desired tint staterequires application of a hold voltage.

“Drive Voltage” refers to the applied voltage provided during at least aportion of the optical transition. The drive voltage may be viewed as“driving” at least a portion of the optical transition. Its magnitude isdifferent from that of the applied voltage immediately prior to thestart of the optical transition. In certain embodiments, the magnitudeof the drive voltage is greater than the magnitude of the hold voltage.An example application of drive and hold voltages is depicted in FIG. 3.

Introduction and Overview

A switchable optical device such as an electrochromic device reversiblycycles between two or more optical states such as a clear state and atinted state. Switching between these states is controlled by applyingpredefined current and/or voltage to the device. The device controllertypically includes a low voltage electrical source and may be configuredto operate in conjunction with radiant and other environmental sensors,although these are not required in various embodiments. The controllermay also be configured to interface with an energy management system,such as a computer system that controls the electrochromic deviceaccording to factors such as the time of year, time of day, securityconditions, and measured environmental conditions. Such an energymanagement system can dramatically lower the energy consumption of abuilding.

In various embodiments herein, an optical transition is influencedthrough feedback that is generated and utilized during the opticaltransition. The feedback may be based on a variety of non-opticalproperties, for example electrical properties. In particular examplesthe feedback may be a current and/or voltage response of an EC devicebased on particular conditions applied to the device. The feedback maybe used to determine or control the tint level in the device, or toprevent damage to the device. In many cases, feedback that isgenerated/obtained during the optical transition is used to adjust theelectrical parameters driving the transition. The disclosed embodimentsprovide a number of ways that such feedback may be used.

FIG. 1 shows a current profile for an electrochromic window employing asimple voltage control algorithm to cause an optical state transition(e.g., tinting) of an electrochromic device. In the graph, ionic currentdensity (I) is represented as a function of time. Many different typesof electrochromic devices will have the depicted current profile. In oneexample, a cathodic electrochromic material such as tungsten oxide isused in conjunction with a nickel tungsten oxide counter electrode. Insuch devices, negative currents indicate tinting of the device. Thespecific depicted profile results by ramping up the voltage to a setlevel and then holding the voltage to maintain the optical state.

The current peaks 101 are associated with changes in optical state,i.e., tinting and clearing. Specifically, the current peaks representdelivery of the charge needed to tint or clear the device.Mathematically, the shaded area under the peak represents the totalcharge required to tint or clear the device. The portions of the curveafter the initial current spikes (portions 103) represent leakagecurrent while the device is in the new optical state.

In FIG. 1, a voltage profile 105 is superimposed on the current curve.The voltage profile follows the sequence: negative ramp (107), negativehold (109), positive ramp (111), and positive hold (113). Note that thevoltage remains constant after reaching its maximum magnitude and duringthe length of time that the device remains in its defined optical state.Voltage ramp 107 drives the device to its new tinted state and voltagehold 109 maintains the device in the tinted state until voltage ramp 111in the opposite direction drives the transition from tinted to clearstates. In some switching algorithms, a current cap is imposed. That is,the current is not permitted to exceed a defined level in order toprevent damaging the device.

The speed of tinting is a function of not only the applied voltage, butalso the temperature and the voltage ramping rate. Since both voltageand temperature affect lithium diffusion, the amount of charge passed(and hence the intensity of this current peak) increases with voltageand temperature as indicated in FIG. 2. Additionally by definition thevoltage and temperature are interdependent, which implies that a lowervoltage can be used at higher temperatures to attain the same switchingspeed as a higher voltage at lower temperatures. This temperatureresponse may be employed in a voltage based switching algorithm butrequires active monitoring of temperature to vary the applied voltage.The temperature is used to determine which voltage to apply in order toeffect rapid switching without damaging the device.

As noted above, various embodiments herein utilize some form of feedbackto actively control a transition in an optically switchable device. Inmany cases the feedback is based on non-optical characteristics.Electrical characteristics are particularly useful, for example voltageand current responses of the optically switchable device when certainelectrical conditions are applied. A number of different uses for thefeedback are provided below.

Controlling a Transition using Electrical Feedback to Ensure SafeOperating Conditions

In some embodiments, electrical feedback is used to ensure that theoptically switchable device is maintained within a safe window ofoperating conditions. If the current or voltage supplied to a device istoo great, it can cause damage to the device. The feedback methodspresented in this section may be referred to as damage preventionfeedback methods. In some embodiments, the damage prevention feedbackmay be the only feedback used. Alternatively, the damage preventionfeedback methods may be combined with other feedback methods describedherein. In other embodiments, the damage prevention feedback is notused, but a different type of feedback described below is used.

FIG. 2 shows a family of Q versus T (charge versus temperature) curvesfor particular voltages. More specifically the figure shows the effectof temperature on how much charge is passed to an electrochromic deviceelectrode after a fixed period of time has elapsed while a fixed voltageis applied. As the voltage increases, the amount of charge passedincreases for a given temperature. Thus, for a desired amount of chargeto be passed, any voltage in a range of voltages might then beappropriate as shown by horizontal line 207 in FIG. 2. And it is clearthat simply controlling the voltage will not guarantee that the changein optical state occurs within a predefined period of time. The devicetemperature strongly influences the current at a particular voltage. Ofcourse, if the temperature of the device is known, then the appliedvoltage can be chosen to drive the tinting change during the desiredperiod of time. However, in some cases it is not possible to reliablydetermine the temperature of the electrochromic device. While the devicecontroller typically knows how much charge is required to switch thedevice, it might not know the temperature.

If too high of a voltage or current is applied for the electrochromicdevice's temperature, then the device may be damaged or degraded. On theother hand, if too low of a voltage or current is applied for thetemperature, then the device will switch too slowly. Thus it would bedesirable to have a controlled current and/or voltage early in theoptical transition. With this in mind, in one embodiment the charge (byway of current) is controlled without being constrained to a particularvoltage.

Some control procedures described herein may be implemented by imposingthe following constraints on the device during an optical transition:(1) a defined amount of charge is passed between the device electrodesto cause a full optical transition; (2) this charge is passed within adefined time frame; (3) the current does not exceed a maximum current;and (4) the voltage does not exceed a maximum voltage.

In accordance with various embodiments described herein, anelectrochromic device is switched using a single algorithm irrespectiveof temperature. In one example, a control algorithm involves (i)controlling current instead of voltage during an initial switchingperiod where ionic current is significantly greater than the leakagecurrent and (ii) during this initial period, employing a current-timecorrelation such that the device switches fast enough at lowtemperatures while not damaging the part at higher temperatures.

Thus, during the transition from one optical state to another, acontroller and an associated control algorithm controls the current tothe device in a manner ensuring that the switching speed is sufficientlyfast and that the current does not exceed a value that would damage thedevice. Further, in various embodiments, the controller and controlalgorithm effects switching in two stages: a first stage that controlscurrent until reaching a defined point prior to completion of theswitching, and a second stage, after the first stage, that controls thevoltage applied to the device.

Various embodiments described herein may be generally characterized bythe following three regime methodology.

1. Control the current to maintain it within a bounded range ofcurrents. This may be done only for a short period of time duringinitiation of the change in optical state. It is intended to protect thedevice from damage due to high current conditions while ensuring thatsufficient current is applied to permit rapid change in optical state.Generally, the voltage during this phase stays within a maximum safevoltage for the device. In some embodiments employing residential orarchitectural glass, this initial controlled current phase will lastabout 3-4 minutes. During this phase, the current profile may berelatively flat, not varying by more than, for example, about 10%.

2. After the initial controlled current stage is complete, there is atransition to a controlled voltage stage where the voltage is held at asubstantially fixed value until the optical transition is complete,i.e., until sufficient charge is passed to complete the opticaltransition. In some cases, the transition from stages 1 to 2 (controlledcurrent to controlled voltage) is triggered by reaching a defined timefrom initiation of the switching operation. In alternative embodiments,however, the transition is accompanied by reaching a predefined voltage,a predefined amount of charge passed, or some other criterion. Duringthe controlled voltage stage, the voltage may be held at a level thatdoes not vary by more than about 0.2 V.

3. After the second stage is completed, typically when the opticaltransition is complete, the voltage is dropped in order to minimize(account for) leakage current while maintaining the new optical state.That is, a small voltage, sometimes referred to as a “hold voltage” isapplied to compensate for a leakage current across the ion conductorlayer. In some embodiments, the leakage current of the EC device can bequite low, e.g. on the order of <1 μA/cm², so the hold voltage is alsosmall. The hold voltage need only compensate for the leakage currentthat would otherwise untint the device due to concomitant ion transferacross the IC layer. The transition to this third stage may be triggeredby, e.g., reaching a defined time from the initiation of the switchingoperation. In other example, the transition is triggered by passing apredefined amount of charge.

FIGS. 3A and 3B show current and voltage profiles resulting for aspecific control method in accordance with certain embodiments. FIG. 3Cprovides an associated flow chart for an initial portion (the controlledcurrent portion) of the control sequence. For purposes of discussion,the negative current shown in these figures, as in FIG. 1, is assumed todrive the clear to tinted transition. Of course, the example could applyequally to devices that operate in reverse, i.e., devices employinganodic electrochromic electrodes.

In a specific example, the following procedure is followed:

1. At time 0 (t₀)—Ramp the voltage at a rate intended to correspond to acurrent level “I target” 301. See block 351 of FIG. 3C. See also avoltage ramp 303 in FIG. 3A. I target may be set a priori for the devicein question—independent of temperature. As mentioned, the control methoddescribed in this section may be beneficially implemented withoutknowing or inferring the device's temperature. In alternativeembodiments, the temperature is detected and considered in setting thecurrent level. In some cases, temperature may be inferred from thecurrent-voltage response of the window.

In some examples, the ramp rate is between about 10 μV/s and 100V/s. Inmore specific examples, the ramp rate is between about 1 mV/s and 500mV/s.

2. Immediately after t₀, typically within a few milliseconds, thecontroller determines the current level resulting from application ofvoltage in operation 1. The resulting current level may be used asfeedback in controlling the optical transition. In particular, theresulting current level may be compared against a range of acceptablecurrents bounded by I slow at the lower end and I safe at the upper end.I safe is the current level above which the device can become damaged ordegraded. I slow is the current level below which the device will switchat an unacceptably slow rate. As an example, I target in anelectrochromic window may be between about 30 and 70 μA/cm². Further,typical examples of I slow range between about 1 and 30 μA/cm² andexamples of I safe range between about 70 and 250 μA/cm².

The voltage ramp is set, and adjusted as necessary, to control thecurrent and typically produces a relatively consistent current level inthe initial phase of the control sequence. This is illustrated by theflat current profile 301 as shown in FIGS. 3A and 3B, which is bracketedbetween levels I safe 307 and I slow 309.

3. Depending upon the results of the comparison in step 2, the controlmethod employs one of the operations (a)-(c) below. Note that thecontroller not only checks the current level immediately after t₀, butit frequently checks the current level thereafter and makes adjustmentsas described here and as shown in FIG. 3C.

(a) Where the measured current is between I slow and I safe→Continue toapply a voltage that maintains the current between I slow and I safe.See the loop defined by blocks 353, 355, 359, 369, and 351 of FIG. 3C.

(b) Where the measured current is below I slow (typically because thedevice temperature is low)→continue to ramp the applied voltage in orderto bring the current above I slow but below I safe. See the loop ofblock 353 and 351 of FIG. 3C. If the current level is too low, it may beappropriate to increase the rate of increase of the voltage (i.e.,increase the steepness of the voltage ramp).

As indicated, the controller typically actively monitors current andvoltage to ensure that the applied current remains above I slow. Thisfeedback helps ensure that the device remains within a safe operatingwindow. In one example, the controller checks the current and/or voltageevery few milliseconds. It may adjust the voltage on the same timescale. The controller may also ensure that the new increased level ofapplied voltage remains below V safe. V safe is the maximum appliedvoltage magnitude, beyond which the device may become damaged ordegraded.

(c) Where the measured current is above I safe (typically because thedevice is operating at a high temperature)→decrease voltage (or rate ofincrease in the voltage) in order to bring the current below I safe butabove I slow. See block 355 and 357 of FIG. 3C. As mentioned, thecontroller may actively monitor current and voltage. As such, thecontroller can quickly adjust the applied voltage to ensure that thecurrent remains below I safe during the entire controlled current phaseof the transition. Thus, the current should not exceed I safe.

As should be apparent, the voltage ramp 303 may be adjusted or evenstopped temporarily as necessary to maintain the current between I slowand I safe. For example, the voltage ramp may be stopped, reversed indirection, slowed in rate, or increased in rate while in the controlledcurrent regime.

In other embodiments, the controller increases and/or decreases current,rather than voltage, as desired. Hence the above discussion should notbe viewed as limiting to the option of ramping or otherwise controllingvoltage to maintain current in the desired range. Whether voltage orcurrent is controlled by the hardware (potentiostatic or galvanostaticcontrol), the algorithm attains the desired result.

4. Maintain current in the target range, between I slow and I safe untila specified criterion is met. In one example, the criterion is passingcurrent for a defined length of time, t₁, at which time the devicereaches a defined voltage V₁. Upon achieving this condition, thecontroller transitions from controlled current to controlled voltage.See blocks 359 and 361 of FIG. 3C. Note that V₁ is a function oftemperature, but as mentioned temperature need not be monitored or evendetected in accordance with various embodiments.

In certain embodiments t₁ is about 1 to 30 minutes, and in some specificexamples t₁ is about 2 to 5 minutes. Further, in some cases themagnitude of V₁ is about 1 to 7 volts, and more specifically about 2.5to 4 volts.

As mentioned the controller continues in the controlled current phaseuntil a specified condition is met such as the passing of a definedperiod of time. In this example, a timer is used to trigger thetransition. In other examples, the specified condition is reaching adefined voltage (e.g., a maximum safe voltage) or passing of a definedamount of charge.

Operations 1-4 correspond to regime 1 in the above generalalgorithm—controlled current. The goal during this phase is to preventthe current from exceeding a safe level while ensuring a reasonablyrapid switching speed. It is possible that during this regime, thecontroller could supply a voltage exceeding the maximum safe voltage forthe electrochromic device. In certain embodiments, this concern iseliminated by employing a control algorithm in which the maximum safevalue is much greater than V₁ across the operational temperature range.In some examples, I target and t₁ are chosen such that V₁ is well belowthe maximum voltage at lower temperatures while not degrading the windowdue to excessive current at higher temperatures. In some embodiments,the controller includes a safety feature that will alarm the windowbefore the maximum safe voltage is reached. In a typical example, thevalue of the maximum safe voltage for an electrochromic window isbetween about 5 and 9 volts.

5. Maintain the voltage at a defined level V₂ until another specifiedcondition is met such as reaching a time t₂. See voltage segment 313 inFIG. 3A. Typically the time t₂ or other specified condition is chosensuch that a desired amount charge is passed sufficient to cause thedesired change in optical state. In one example, the specified conditionis passage of a pre-specified amount of charge. During this phase, thecurrent may gradually decrease as illustrated by current profile segment315 in FIGS. 3A and 3B. In a specific embodiment, V₂=V₁, as is shown inFIG. 3A.

This operation 5 corresponds to the regime 2 above—controlled voltage. Agoal during this phase is to maintain the voltage at V₁ for a sufficientlength to ensure a desired tinting speed.

In certain embodiments t₂ is about 2 to 30 minutes, and in some specificexamples t₂ is about 3 to 10 minutes. Further, in some cases V₂ is about1 to 7 volts, and more specifically about 2.5 to 4 volts.

6. After the condition of step 5 is reached (e.g., after sufficientcharge has passed or a timer indicates t₂ has been reached), the voltageis dropped from V₂ to a level V₃. This reduces leakage current duringwhile the tinted state is held. In a specific embodiment, the transitiontime t₂ is predetermined and chosen based on the time required for thecenter of the part, which is the slowest to tint, to reach a certainpercent transmissivity. In some embodiments, the t₂ is between about 4and 6 minutes. This operation 6 corresponds to regime 3 above.

Table 1 presents a specific example of the algorithm described above.

TABLE 1 Variable Fixed End Time Current Voltage parameter parameterConstraints Condition 0 0 0 None t0 to t1 I0 = I target V0 to V1 V0, V1t1, I target I slow < t > t1 I0 < I safe t1 to t2 I1 to I2 V2 = V1 I2t2, V2 None t > t2 t2 to t3 I2 to I3 V3 I3 V3 None State change requestDefinition of parameters: I0—targeted current value between I slow and Isafe V0—voltage corresponding to current I₀ T0—time at which current =I0. I1—current at time t1. I1 = I0 V1—voltage at time t1. Voltage rampsfrom V0 to V1 between t0 and t1 and is a function of temperature.t1—time for which current is maintained between I slow and I safe (e.g.,about 3-4 minutes) I2—current at time t2. Current decays from I1 to I2when voltage is maintained at V1. V2—voltage at time t2. V1 = V2.t2—time till which voltage V1 is maintained. May be between about 4 to 6min from t1. After t2 the voltage is dropped from V2 to V3 V3—holdvoltage between t2 and t3. I3—current corresponding to voltage V3.t3—time at which state change request is received.

Controlling a Transition Using Electrical Feedback to Determine the EndPoint of a Transition

Embodiments described in this regard relate to the use of electricalfeedback in determining the end point of a transition. In other words,feedback is used to determine when an optical transition is complete ornearly complete. These feedback methods may be used alone or incombination with other feedback methods described herein.

Certain disclosed embodiments make use of electrical probing andmonitoring to determine when an optical transition between a firstoptical state and a second optical state of an optically switchabledevice has proceeded to a sufficient extent that the application of adrive voltage can be terminated. For example, electrical probing allowsfor application of drive voltages for less time than previously thoughtpossible, as a particular device is driven based on electrical probingof its actual optical transition progression in real time. Further, realtime monitoring can help ensure that an optical transition progresses toa desired state. In various embodiments, terminating the drive voltageis accomplished by dropping the applied voltage to a hold voltage. Thisapproach takes advantage of an aspect of optical transitions that istypically considered undesirable—the propensity of thin opticallyswitchable devices to transition between optical states non-uniformly.In particular, many optically switchable devices initially transition atlocations close to the bus bars and only later at regions far from thebus bars (e.g., near the center of the device). Surprisingly, thisnon-uniformity can be harnessed to probe the optical transition. Byallowing the transition to be probed in the manner described herein,optically switchable devices avoid the need for custom characterizationand associated preprogramming of device control algorithms specifyingthe length of time a drive voltage is applied as well as obviating “onesize fits all” fixed time period drive parameters that account forvariations in temperature, device structure variability, and the likeacross many devices. Before describing probing and monitoring techniquesin more detail, some context on optical transitions in electrochromicdevices will be provided.

Driving a transition in a typical electrochromic device is accomplishedby applying a defined voltage to two separated bus bars on the device.In such a device, it is convenient to position bus bars perpendicular tothe smaller dimension of a rectangular window (see FIG. 4A). This isbecause the transparent conducting layers used to deliver an appliedvoltage over the face of the thin film device have an associated sheetresistance, and the bus bar arrangement allows for the shortest spanover which current must travel to cover the entire area of the device,thus lowering the time it takes for the conductor layers to be fullycharged across their respective areas, and thus lowering the time totransition the device.

While an applied voltage, V_(app), is supplied across the bus bars,essentially all areas of the device see a lower local effective voltage(V_(eff)) due to the sheet resistance of the transparent conductinglayers and the current draw of the device. The center of the device (theposition midway between the two bus bars) frequently has the lowestvalue of V_(eff). This may result in an unacceptably small opticalswitching range and/or an unacceptably slow switching time in the centerof the device. These problems may not exist at the edges of the device,nearer the bus bars. This is explained in more detail below withreference to FIGS. 4B and 4C.

FIG. 4A shows a top-down view of an electrochromic lite 400 includingbus bars having a planar configuration. Electrochromic lite 400 includesa first bus bar 405 disposed on a first conductive layer 410 and asecond bus bar 415 disposed on a second conductive layer, 420. Anelectrochromic stack (not shown) is sandwiched between first conductivelayer 410 and second conductive layer 420. As shown, first bus bar 405may extend substantially across one side of first conductive layer 410.Second bus bar 415 may extend substantially across one side of secondconductive layer 420 opposite the side of electrochromic lite 400 onwhich first bus bar 405 is disposed. Some devices may have extra busbars, e.g., on all four edges, but this complicates fabrication. Afurther discussion of bus bar configurations, including planarconfigured bus bars, is found in U.S. patent application Ser. No.13/452,032 filed Apr. 20, 2012, which is incorporated herein byreference in its entirety.

FIG. 4B is a graph showing a plot of the local voltage in firsttransparent conductive layer 410 and the voltage in second transparentconductive layer 420 that drives the transition of electrochromic lite400 from a clear state to a tinted state, for example. Plot 425 showsthe local values of the voltage V_(TCL) in first transparent conductivelayer 410. As shown, the voltage drops from the left hand side (e.g.,where first bus bar 405 is disposed on first conductive layer 410 andwhere the voltage is applied) to the right hand side of first conductivelayer 410 due to the sheet resistance and current passing through firstconductive layer 410. Plot 430 also shows the local voltage V_(TCL) insecond conductive layer 420. As shown, the voltage increases (decreasesin magnitude) from the right hand side (e.g., where second bus bar 415is disposed on second conductive layer 420 and where the voltage isapplied) to the left hand side of second conductive layer 420 due to thesheet resistance of second conductive layer 420. The value of theapplied voltage, V_(app), in this example is the difference in voltagebetween the right end of potential plot 430 and the left end ofpotential plot 425. The value of the effective voltage, V_(eff), at anylocation between the bus bars is the difference in values of curves 430and 425 at the position on the x-axis corresponding to the location ofinterest.

FIG. 4C is a graph showing a plot of V_(eff) across the electrochromicdevice between first and second conductive layers 410 and 420 ofelectrochromic lite 400. As explained, the effective voltage is thelocal voltage difference between the first conductive layer 410 and thesecond conductive layer 420. Regions of an electrochromic devicesubjected to higher effective voltages transition between optical statesfaster than regions subjected to lower effective voltages. As shown, theeffective voltage is the lowest at the center of electrochromic lite 400and highest at the edges of electrochromic lite 400. The voltage dropacross the device is due to ohmic losses as current passes through thedevice. The voltage drop across large electrochromic windows can bealleviated by configuring additional bus bars within the viewing area ofthe window, in effect dividing one large optical window into multiplesmaller electrochromic windows which can be driven in series orparallel. However, this approach may not be aesthetically appealing dueto the contrast between the viewable area and the bus bar(s) in theviewable area. That is, it may be much more pleasing to the eye to havea monolithic electrochromic device without any distracting bus bars inthe viewable area.

As described above, as the window size increases, the electronicresistance to current flowing across the thin face of the TC layers alsoincreases. This resistance may be measured between the points closest tothe bus bar (referred to as edge of the device in following description)and in the points furthest away from the bus bars (referred to as thecenter of the device in following description). When current passesthrough a TCL, the voltage drops across the TCL face and this reducesthe effective voltage at the center of the device. This effect isexacerbated by the fact that typically as window area increases, theleakage current density for the window stays constant but the totalleakage current increases due to the increased area. Thus with both ofthese effects the effective voltage at the center of the electrochromicwindow falls substantially, and poor performance may be observed forelectrochromic windows which are larger than, for example, about 30inches across. This issue can be addressed by using a higher V_(app)such that the center of the device reaches a suitable effective voltage.

Typically the range of safe operation for solid state electrochromicdevices is between about 0.5V and 4V, or more typically between about0.8V and about 3V, e.g. between 0.9V and 1.8V. These are local values ofV_(eff). In one embodiment, an electrochromic device controller orcontrol algorithm provides a driving profile where V_(eff) is alwaysbelow 3V, in another embodiment, the controller controls V_(eff) so thatit is always below 2.5V, in another embodiment, the controller controlsV_(eff) so that it is always below 1.8V. The recited voltage valuesrefer to the time averaged voltage (where the averaging time is of theorder of time required for small optical response, e.g., few seconds tofew minutes).

An added complexity of electrochromic windows is that the current drawnthrough the window is not fixed over the duration of the opticaltransition. Instead, during the initial part of the transition, thecurrent through the device is substantially larger (up to 100× larger)than in the end state when the optical transition is complete or nearlycomplete. The problem of poor tinting in center of the device is furtherexacerbated during this initial transition period, as the value V_(eff)at the center is significantly lower than what it will be at the end ofthe transition period.

In the case of an electrochromic device with a planar bus bar, it can beshown that the V_(eff) across a device with planar bus bars is generallygiven by:

ΔV(0)=V _(app) −RJL ²/2

ΔV(L)=V _(app) −RJL ²/2

ΔV(L/2)=V _(app)−3RJL ²/4  Equation 1

where:V_(app) is the voltage difference applied to the bus bars to drive theelectrochromic window;ΔV(0) is V_(eff) at the bus bar connected to the first transparentconducting layer (in the example below, TEC type TCO);ΔV(L) is V_(eff) at the bus bar connected to the second transparentconducting layer (in the example below, ITO type TCO);ΔV(L/2) is V_(eff) at the center of the device, midway between the twoplanar bus bars;R=transparent conducting layer sheet resistance;J=instantaneous average current density; andL=distance between the bus bars of the electrochromic device.

The transparent conducting layers are assumed to have substantiallysimilar, if not the same, sheet resistance for the calculation. Howeverthose of ordinary skill in the art will appreciate that the applicablephysics of the ohmic voltage drop and local effective voltage stillapply even if the transparent conducting layers have dissimilar sheetresistances.

As noted, certain embodiments pertain to controllers and controlalgorithms for driving optical transitions in devices having planar busbars. In such devices, substantially linear bus bars of oppositepolarity are disposed at opposite sides of a rectangular or otherpolygonally shaped electrochromic device, as shown in FIG. 4a , forinstance. In some embodiments, devices with non-planar bus bars may beemployed. Such devices may employ, for example, angled bus bars disposedat vertices of the device. In such devices, the bus bar effectiveseparation distance, L, is determined based on the geometry of thedevice and bus bars. A discussion of bus bar geometries and separationdistances may be found in U.S. patent application Ser. No. 13/452,032,entitled “Angled Bus Bar”, and filed Apr. 20, 2012, which isincorporated herein by reference in its entirety.

As R, J or L increase, V_(eff) across the device decreases, therebyslowing or reducing the device tinting during transition and even in thefinal optical state. Referring to Equation 1, the V_(eff) across thewindow is at least RJL²/2 lower than V_(app). It has been found that asthe resistive voltage drop increases (due to increase in the windowsize, current draw etc.) some of the loss can be negated by increasingV_(app) but doing so only to a value that keeps V_(eff) at the edges ofthe device below the threshold where reliability degradation wouldoccur.

In summary, it has been recognized that both transparent conductinglayers experience ohmic drop, and that drop increases with distance fromthe associated bus bar, and therefore V_(TCL) decreases with distancefrom the bus bar for both transparent conductive layers. As aconsequence V_(eff) decreases in locations removed from both bus bars.

FIG. 5 illustrates a voltage control profile in accordance with certainembodiments. In the depicted embodiment, a voltage control profile isemployed to drive the transition from a clear state to a tinted state(or to an intermediate state). To drive an electrochromic device in thereverse direction, from a tinted state to a clear state (or from a moretinted to less tinted state), a similar but inverted profile is used. Insome embodiments, the voltage control profile for going from tinted toclear is a mirror image of the one depicted in FIG. 5.

The voltage values depicted in FIG. 5 represent the applied voltage(V_(app)) values. The applied voltage profile is shown by the dashedline. For contrast, the current density in the device is shown by thesolid line. In the depicted profile, V_(app) includes four components: aramp to drive component 503, which initiates the transition, a V_(drive)component 513, which continues to drive the transition, a ramp to holdcomponent 515, and a V_(hold) component 517. The ramp components areimplemented as variations in V_(app) and the V_(drive) and V_(hold)components provide constant or substantially constant V_(app)magnitudes.

The ramp to drive component is characterized by a ramp rate (increasingmagnitude) and a magnitude of V_(drive). When the magnitude of theapplied voltage reaches V_(drive), the ramp to drive component iscompleted. The V_(drive) component is characterized by the value ofV_(drive) as well as the duration of V_(drive). The magnitude ofV_(drive) may be chosen to maintain V_(eff) with a safe but effectiverange over the entire face of the electrochromic device as describedabove.

The ramp to hold component is characterized by a voltage ramp rate(decreasing magnitude) and the value of V_(hold) (or optionally thedifference between V_(drive) and V_(hold)). V_(app) drops according tothe ramp rate until the value of V_(hold) is reached. The V_(hold)component is characterized by the magnitude of V_(hold) and the durationof V_(hold). Actually, the duration of V_(hold) is typically governed bythe length of time that the device is held in the tinted state (orconversely in the clear state). Unlike the ramp to drive, V_(drive), andramp to hold components, the V_(hold) component has an arbitrary length,which is independent of the physics of the optical transition of thedevice.

Each type of electrochromic device will have its own characteristiccomponents of the voltage profile for driving the optical transition.For example, a relatively large device and/or one with a more resistiveconductive layer will require a higher value of V_(drive) and possibly ahigher ramp rate in the ramp to drive component. U.S. patent applicationSer. No. 13/449,251, filed Apr. 17, 2012, and incorporated herein byreference, discloses controllers and associated algorithms for drivingoptical transitions over a wide range of conditions. As explainedtherein, each of the components of an applied voltage profile (ramp todrive, V_(drive), ramp to hold, and V_(hold), herein) may beindependently controlled to address real-time conditions such as currenttemperature, current level of transmissivity, etc. In some embodiments,the values of each component of the applied voltage profile is set for aparticular electrochromic device (having its own bus bar separation,resistivity, etc.) and does not vary based on current conditions. Inother words, in such embodiments, the voltage profile does not take intoaccount feedback such as temperature, current density, and the like.

As indicated, all voltage values shown in the voltage transition profileof FIG. 5 correspond to the V_(app) values described above. They do notcorrespond to the V_(eff) values described above. In other words, thevoltage values depicted in FIG. 5 are representative of the voltagedifference between the bus bars of opposite polarity on theelectrochromic device.

In certain embodiments, the ramp to drive component of the voltageprofile is chosen to safely but rapidly induce ionic current to flowbetween the electrochromic and counter electrodes. As shown in FIG. 5,the current in the device follows the profile of the ramp to drivevoltage component until the ramp to drive portion of the profile endsand the V_(drive) portion begins. See current component 501 in FIG. 5.Safe levels of current and voltage can be determined empirically orbased on other feedback. Examples of safe current and voltage levels areprovided above.

In certain embodiments, the value of V_(drive) is chosen based on theconsiderations described above. Particularly, it is chosen so that thevalue of V_(eff) over the entire surface of the electrochromic deviceremains within a range that effectively and safely transitions largeelectrochromic devices. The duration of V_(drive) can be chosen based onvarious considerations. One of these ensures that the drive potential isheld for a period sufficient to cause the substantial tinting of thedevice. For this purpose, the duration of V_(drive) may be determinedempirically, by monitoring the optical density of the device as afunction of the length of time that V_(drive) remains in place. In someembodiments, the duration of V_(drive) is set to a specified timeperiod. In another embodiment, the duration of V_(drive) is set tocorrespond to a desired amount of ionic and/or electronic charge beingpassed. As shown, the current ramps down during V_(drive). See currentsegment 507.

Another consideration is the reduction in current density in the deviceas the ionic current decays as a consequence of the available lithiumions completing their journey from the anodic coloring electrode to thecathodic coloring electrode (or counter electrode) during the opticaltransition. When the transition is complete, the only current flowingacross device is leakage current through the ion conducting layer. As aconsequence, the ohmic drop in potential across the face of the devicedecreases and the local values of V_(eff) increase. These increasedvalues of V_(eff) can damage or degrade the device if the appliedvoltage is not reduced. Thus, another consideration in determining theduration of V_(drive) is the goal of reducing the level of V_(eff)associated with leakage current. By dropping the applied voltage fromV_(drive) to V_(hold), not only is V_(eff) reduced on the face of thedevice but leakage current decreases as well. As shown in FIG. 5, thedevice current transitions in a segment 505 during the ramp to holdcomponent. The current settles to a stable leakage current 509 duringV_(hold).”

A challenge arises because it can be difficult to predict how long theapplied drive voltage should be applied before transitioning to the holdvoltage. Devices of different sizes, and more particularly deviceshaving bus bars separated by particular distances, require differentlengths of time for applying the drive voltage. Further, the processesemployed to fabricate optically switchable devices such aselectrochromic devices may vary subtly from one batch to another or oneprocess revision to another. The subtle process variations translateinto potentially different requirements for the length of time that thedrive voltage must be applied to the devices used in operation. Stillfurther, environmental conditions, and particularly temperature, caninfluence the length of time that the applied voltage should be appliedto drive the transition, for the reasons discussed above with referenceto FIG. 2, for example.

To account for all these variables, current technology may define manydistinct control algorithms with distinct periods of time for applying adefined drive voltage for each of many different window sizes or devicefeatures. A rationale for doing this is to ensure that the drive voltageis applied for a sufficient period, regardless of device size and type,to ensure that the optical transition is complete. Currently manydifferent sized electrochromic windows are manufactured. While it ispossible to pre-determine the appropriate drive voltage time for eachand every different type of window, this can be a tedious, expensive,and time-consuming process. An improved approach, described here, is todetermine on-the-fly the length of time that the drive voltage should beapplied.

Further, it may be desirable to cause the transition between two definedoptical states to occur within a defined duration, regardless of thesize of the optically switchable device, the process under which thedevice is fabricated, and the environmental conditions in which thedevice is operating at the time of the transition. This goal can berealized by monitoring the course of the transition and adjusting thedrive voltage as necessary to ensure that the transition completes inthe defined time. Adjusting the magnitude of the drive voltage is oneway of accomplishing this. Such methods are discussed further below inthe section regarding Controlling a Transition using Electrical Feedbackto Determine the End Point of a Transition.

Certain disclosed embodiments apply a probing technique to assess theprogress of an optical transition while the device is in transition. Asillustrated in FIG. 5, there are typically distinct ramp to drive anddrive voltage maintenance stages of the optical transition. The probetechnique can be applied during either of these stages. In manyembodiments, the probing technique is applied during the drive voltagemaintenance portion of the algorithm.

In certain embodiments, the probing technique involves pulsing thecurrent or voltage applied to drive the transition and then monitoringthe current or voltage response to detect an overdrive condition in thevicinity of the bus bars. An overdrive condition occurs when the localeffective voltage is greater than needed to cause a local opticaltransition. For example, if an optical transition to a clear state isdeemed complete when V_(eff) reaches 2V, and the local value of V_(eff)near a bus bar is 2.2V, the position near the bus bar may becharacterized as in an overdrive condition.

One example of a probing technique involves pulsing the applied drivevoltage by dropping it to the level of the hold voltage (or the holdvoltage modified by an appropriate offset) and monitoring the currentresponse to determine the direction of the current response. In thisexample, when the current response reaches a defined threshold, thedevice control system determines that it is now time to transition fromthe drive voltage to the hold voltage.

FIG. 6A is a graph depicting an optical transition in which a drop inapplied voltage from V_(drive) to V_(hold) results in a net current flowestablishing that the optical transition has proceeded far enough topermit the applied voltage to remain at V_(hold) for the duration of theending optical state. This is illustrated by a voltage drop 611 inV_(app) from V_(drive) to V_(hold). Voltage drop 611 is performed duringa period when the V_(app) might otherwise be constrained to remain inthe drive phase shown in FIG. 5. The current flowing between the busbars began dropping (becoming less negative), as illustrated by currentsegment 507, when the applied voltage initially stopped increasing(becoming more negative) and plateaued at V_(drive). However, when theapplied voltage now dropped at 611, the current began decreasing morereadily as illustrated by current segment 615. In accordance with someembodiments, the level of current is measured after a defined period oftime passes following the voltage drop 611. If the current is below acertain threshold, the optical transition is deemed complete, and theapplied voltage may remain at V_(hold) (or move to V_(hold) if it is atsome other level below V_(drive)). In the particular example of FIG. 6A,the current threshold is exceeded as illustrated. Therefore, the V_(app)remains at V_(hold). for the duration of the ending optical state.V_(hold) may be selected for the ending optical state it provides. Suchending optical state may be a maximum, minimum, or intermediate opticalstate for the optical device undergoing the transition.

In situations where the current does not reach the threshold whenmeasured, it may be appropriate to return V_(app) to V_(drive). FIG. 6Billustrates this situation. FIG. 6B is a graph depicting an opticaltransition in which an initial drop in applied voltage from V_(drive) toV_(hold) (see 611) results in a net current flow indicating that theoptical transition has not yet proceeded far enough to permit theapplied voltage to remain at V_(hold) for the duration of the endingoptical state. Note that current segment 615, which has a trajectoryresulting from voltage drop 611, does not reach the threshold whenprobed at 619. Therefore the applied voltage is returned to V_(drive)for a further period of time—while the current recovers at 617—beforeagain dropping to V_(hold) (621) at which point the resulting current(623) establishes that the optical transition has proceeded far enoughto permit the applied voltage to remain at V_(hold) for the duration ofthe ending optical state. As explained, the ending optical state may bea maximum, minimum, or intermediate optical state for the optical deviceundergoing the transition.

As explained, the hold voltage is a voltage that will maintain theoptical device in equilibrium at a particular optical density or otheroptical condition. It produces a steady-state result by generating acurrent that offsets the leakage current in the ending optical state.The drive voltage is applied to speed the transition to a point whereapplying the hold voltage will result in a time invariant desiredoptical state.

The probing techniques described herein may be understood in terms ofthe physical mechanisms associated with an optical transition drivenfrom bus bars at the edges of a device. Basically, the technique relieson differential values of the effective voltage experienced in theoptically switchable device across the face of the device, andparticularly the variation in V_(eff) from the center of the device tothe edge of the device. The local variation in potential on thetransparent conductive layers results in different values of V_(eff)across the face of the device. The value of V_(eff) experienced by theoptically switchable device near the bus bars is far greater the valueof V_(eff) in the center of the device. As a consequence, the localcharge buildup in the region next to the bus bars is significantlygreater than the charge buildup in the center the device.

At some point during the optical transition, the value of V_(eff) at theedge of the device near the bus bars is sufficient to exceed the endingoptical state desired for the optical transition whereas in the centerof the device, the value of V_(eff) is insufficient to reach that endingstate. The ending state may be an optical density value associated withthe endpoint in the optical transition. While in this intermediate stageof the optical transition, if the drive voltage is dropped to the holdvoltage, the portion of the electrochromic device close to the bus barswill effectively try to transition back toward the state from which itstarted. However, as the device state in the center of the device hasnot yet reached the end state of the optical transition, when a holdvoltage is applied, the center portion of the device will continuetransitioning in the direction desired for the optical transition.

When the device in this intermediate stage of transition experiences thechange in applied voltage from the drive voltage to the hold voltage (orsome other suitably lower magnitude voltage), the portions of the devicelocated near the bus bars—where the device is effectivelyoverdriven—generate current flowing in the direction opposite thatrequired to drive the transition. In contrast, the regions of the devicein the center, which have not yet fully transitioned to the final state,continue to promote current flow in a direction required to drive thetransition.

Over the course of the optical transition, and while the device isexperiencing the applied drive voltage, there is a gradual increase inthe driving force for causing current to flow in the reverse directionwhen the device is subject to a sudden drop in applied voltage. Bymonitoring the flow of current in response to perturbations away fromdrive voltage, one can determine a point at which the transition fromthe first state to the second state is sufficiently far along that atransition from drive voltage to hold voltage is appropriate. By“appropriate,” it is meant that the optical transition is sufficientlycomplete from the edge of the device to the center of the device. Suchtransition can be defined in many ways depending upon the specificationsof the product and its application. In one embodiment, it assumes thatthe transition from the first state to the second state is at leastabout 80% of complete or at least about 95% of complete. Completereflecting the change in optical density from the first state to thesecond state. The desired level of completeness may correspond to athreshold current level as depicted in the examples of FIGS. 6A and 6B.

Many possible variations to the probing protocol exist. Such variationsmay include certain pulse protocols defined in terms of the length oftime from the initiation of the transition to the first pulse, theduration of the pulses, the size of the pulses, and the frequency of thepulses.

In one embodiment, the pulse sequence is begun immediately upon theapplication of a drive voltage or a ramp to drive voltage that initiatesthe transition between the first optical state and second optical state.In other words, there would be no lag time between the initiation of thetransition and the application of pulsing. In some implementations, theprobe duration is sufficiently short (e.g., about 1 second or less) thatprobing back and forth between V_(drive) and V_(hold) for the entiretransition is not significantly detrimental to switching time. However,in some embodiments, it is unnecessary to start probing right away. Insome cases, switching is initiated after about 50% of an expected ornominal switching period is complete, or about 75% of such period iscomplete. Often, the distance between bus bars is known or can be readusing an appropriately configured controller. With the distance known, aconservative lower limit for initiating probing may be implemented basedon approximate known switching time. As an example, the controller maybe configured to initiate probing after about 50-75% of expectedswitching duration is complete.

In some embodiments, the probing begins after about 30 seconds frominitiating the optical transition. Relatively earlier probing may beespecially helpful in cases where an interrupt command is received. Aninterrupt command is one that instructs the device to switch to a thirdoptical transmission state when the device is already in the process ofchanging from a first to a second optical transmission state. In thiscase, early probing can help determine the direction of the transition(i.e., whether the interrupt command requires the window to becomelighter or darker than when the command is received). Methods in whichelectrical feedback is used after receiving an interrupt command arefurther discussed below in the section regarding Controlling aTransition using Electrical Feedback to Transition to a Modified EndState.

In some embodiments, the probing begins about 120 minutes (or about 30minutes, about 60 minutes, or about 90 minutes) after initiating theoptical transition. Relatively later probing may be more useful wherelarger windows are used, and where the transition occurs from anequilibrium state. For architectural glass, probing may begin about 30seconds to 30 minutes after initiating the optical transition, in somecases between about 1-5 minutes, for example between about 1-3 minutes,or between about 10-30 minutes, or between about 20-30 minutes. In someembodiments, the probing begins about 1-5 minutes (e.g., about 1-3minutes, about 2 minutes in a particular example) after initiating anoptical transition through an interrupt command, while the probingbegins about 10-30 minutes (e.g., about 20-30 minutes) after initiatingan optical transition from an initial command given when theelectrochromic device is in an equilibrium state.

In the examples of FIGS. 6A and 6B, the magnitude of the pulses isbetween the drive voltage value and the hold voltage value. This may bedone for convenience. Other pulse magnitudes are possible. For example,the pulse may have a magnitude that falls within about +/−500 mV of thehold voltage, or within about +/−200 mV of the hold voltage. Forcontext, an electrochromic device on a window, such as an architecturalwindow, may have a drive voltage of about 0 V to +/−20 V (e.g., about+/−2 V to +/−10 V) and a hold voltage of about 0 V to +/−4 V (e.g.,about +/−1 V to +/−2 V). In some embodiments, the hold voltage isbetween about +/−1 V to +/−1.5 V.

In various embodiments, the controller determines when during theoptical transition the polarity of the probe current opposes thepolarity of the bias due to the transition proceeding to a significantextent. In other words, the controller detects/determines when currentto the bus bars flows in a direction opposite of what would be expectedif the optical transition was still proceeding.

Probing by dropping the applied voltage magnitude from V_(drive) toV_(hold) provides a convenient, and broadly applicable, mechanism formonitoring the transition to determine when the probe current firstreverses polarity. Probing by dropping the voltage to a magnitude otherthan that of V_(hold) may involve characterization of windowperformance. It appears that even very large windows (e.g., about 60″)essentially complete their optical transition when the current firstopposes the transition upon probing from V_(drive) to V_(hold).

In certain cases, probing occurs by dropping the applied voltagemagnitude from V_(drive) to V_(probe), where V_(probe) is a probevoltage other than the hold voltage. For example, V_(probe) may beV_(hold) as modified by an offset. Although many windows are able toessentially complete their optical transitions when the current firstopposes the transition after probing from V_(drive) to V_(hold), certainwindows may benefit from pulsing to a voltage slightly offset from thehold voltage. In general, the offset becomes increasingly beneficial asthe size of the window increases, and as the temperature of the windowdrops. In certain cases, the offset is between about 0-1 V, and themagnitude of V_(probe) is between about 0-1 V higher than the magnitudeof V_(hold). For example, the offset may be between about 0-0.4 V. Inthese or other embodiments, the offset may be at least about 0.025 V, orat least about 0.05 V, or at least about 0.1 V. The offset may result inthe transition having a longer duration than it otherwise would. Thelonger duration helps ensure that the optical transition is able tofully complete. Techniques for selecting an appropriate offset from thehold voltage are discussed further below in the context of a target opencircuit voltage.

In some embodiments, the controller notifies a user or the windownetwork master controller of how far (by, e.g., percentage) the opticaltransition has progressed. This may be an indication of whattransmission level the center of the window is currently at. Feedbackregarding transition may be provided to user interface in a mobiledevice or other computational apparatus. See e.g., PCT PatentApplication No. US2013/036456 filed Apr. 12, 2013, which is incorporatedherein by reference in its entirety.

The frequency of the probe pulsing may be between about 10 seconds and500 seconds. As used in this context, the “frequency” means theseparation time between the midpoints of adjacent pulses in a sequenceof two or more pulses. Typically, the frequency of the pulsing isbetween about 10 seconds and 120 seconds. In certain embodiments, thefrequency of the pulsing is between about 20 seconds and 30 seconds. Incertain embodiments, the probe frequency is influenced by the size ofthe electrochromic device or the separation between bus bars in thedevice. In certain embodiments, the probe frequency is chosen as afunction the expected duration of the optical transition. For example,the frequency may be set to be about ⅕^(th) to about 1/50^(th) (or about1/10^(th) to about 1/30^(th)) of the expected duration of the transitiontime. Note that transition time may correspond to the expected durationof V_(app)=V_(drive). Note also that the expected duration of thetransition may be a function of the size of the electrochromic device(or separation of bus bars). In one example, the duration for 14″windows is ˜2.5 minutes, while the duration for 60″ windows is ˜40minutes. In one example, the probe frequency is every 6.5 seconds for a14″ window and every 2 minutes for a 60″ window.

In various implementations, the duration of each pulse is between about1×10⁻⁵ and 20 seconds. In some embodiments, the duration of the pulsesis between about 0.1 and 20 seconds, for example between about 0.5seconds and 5 seconds.

As indicated, in certain embodiments, an advantage of certain probingtechniques disclosed herein is that only very little information need bepre-set with the controller that is responsible for controlling a windowtransition. Typically, such information includes only the hold voltage(and voltage offset, if applicable) associated for each optical endstate. Additionally, the controller may specify a difference in voltagebetween the hold voltage and a drive voltage, or alternatively, thevalue of V_(drive) itself. Therefore, for any chosen ending opticalstate, the controller would know the magnitudes of V_(hold), V_(offset)and V_(drive). The duration of the drive voltage may be determined usingthe probing algorithm described here. In other words, the controllerdetermines how to appropriately apply the drive voltage as a consequenceof actively probing the extent of the transition in real time.

FIG. 7A presents a flowchart 701 for a process of monitoring andcontrolling an optical transition in accordance with certain disclosedembodiments. As depicted, the process begins with an operation denotedby reference number 703, where a controller or other control logicreceives instructions to direct the optical transition. As explained,the optical transition may be an optical transition between a tintedstate and a more clear state of electrochromic device. The instructionsfor directing the optical transition may be provided to the controllerbased upon a preprogrammed schedule, an algorithm reacting to externalconditions, manual input from a user, etc. Regardless of how theinstructions originate, the controller acts on them by applying a drivevoltage to the bus bars of the optically switchable device. See theoperation denoted by reference number 705.

As explained above, in conventional embodiments, the drive voltage isapplied to the bus bars for a defined period of time after which it ispresumed that the optical transition is sufficiently complete that theapplied voltage can be dropped to a hold voltage. In such embodiments,the hold voltage is then maintained for the duration of the pendingoptical state. In contrast, in accordance with embodiments disclosedherein, the transition from a starting optical state to an endingoptical state is controlled by probing the condition of the opticallyswitchable device one or more times during the transition. Thisprocedure is reflected in operations 707, et seq. of FIG. 7A.

In operation 707, the magnitude of the applied voltage is dropped afterallowing the optical transition to proceed for an incremental period oftime. The duration of this incremental transition is significantly lessthan the total duration required to fully complete the opticaltransition. Upon dropping the magnitude of the applied voltage, thecontroller measures the response of the current flowing to the bus bars.See operation 709. The relevant controller logic may then determinewhether the current response indicates that the optical transition isnearly complete. See decision 711. As explained above, the determinationof whether an optical transition is nearly complete can be accomplishedin various ways. For example, it may be determined by the currentreaching a particular threshold. Assuming that the current response doesnot indicate that the optical transition is nearly complete, processcontrol is directed to an operation denoted by reference number 713. Inthis operation, the applied voltage is returned to the magnitude of thedrive voltage. Process controls then loops back to operation 707 wherethe optical transition is allowed to proceed by a further incrementbefore again dropping the magnitude of the applied voltage to the busbars.

At some point in the procedure 701, decision operation 711 determinesthat the current response indicates that the optical transition is infact nearly complete. At this point, process control proceeds to anoperation indicated by reference number 715, where the applied voltageis transitioned to or maintained at the hold voltage for the duration ofthe ending optical state. At this point, the process is complete.

FIG. 7B presents a flowchart 701 for a process of monitoring andcontrolling an optical transition in accordance with certain disclosedembodiments. In this case, the process condition probed is the opencircuit voltage, as described in the previous paragraph. The first twodepicted operations in flowchart 741 correspond to the first twooperations in flowcharts 701 and 721. In other words, operations 743 and745 of flowchart 741 correspond to operations 703 and 705 of flowchart701. Briefly, in operation 743, the controller or other appropriatelogic receives instructions to undergo an optical transition. Then, atoperation 745, the controller applies a drive voltage to the bus bars.After allowing the optical transition to proceed incrementally, thecontroller applies open circuit conditions to the electrochromic deviceat operation 747. Next, the controller measures the open circuit voltageresponse at operation 749.

As is the case above, the controller may measure the electronic response(in this case the open circuit voltage) after a defined period haspassed since applying the open circuit conditions. Upon application ofopen circuit conditions, the voltage typically experiences an initialdrop relating to the ohmic losses in external components connected tothe electrochromic device. Such external components may be, for example,conductors and connections to the device. After this initial drop, thevoltage experiences a first relaxation and settles at a first plateauvoltage. The first relaxation relates to internal ohmic losses, forexample over the electrode/electrolyte interfaces within theelectrochromic devices. The voltage at the first plateau corresponds tothe voltage of the cell, with both the equilibrium voltage and theovervoltages of each electrode. After the first voltage plateau, thevoltage experiences a second relaxation to an equilibrium voltage. Thissecond relaxation is much slower, for example on the order of hours. Insome cases it is desirable to measure the open circuit voltage duringthe first plateau, when the voltage is relatively constant for a shortperiod of time. This technique may be beneficial in providing especiallyreliable open circuit voltage readings. In other cases, the open circuitvoltage is measured at some point during the second relaxation. Thistechnique may be beneficial in providing sufficiently reliable opencircuit readings while using less expensive and quick-operatingpower/control equipment.

In some embodiments, the open circuit voltage is measured after a setperiod of time after the open circuit conditions are applied. Theoptimal time period for measuring the open circuit voltage is dependentupon the distance between the bus bars. The set period of time mayrelate to a time at which the voltage of a typical or particular deviceis within the first plateau region described above. In such embodiments,the set period of time may be on the order of milliseconds (e.g., a fewmilliseconds in some examples). In other cases, the set period of timemay relate to a time at which the voltage of a typical or particulardevice is experiencing the second relaxation described above. Here, theset period of time may be on the order of about 1 second to severalseconds, in some cases. Shorter times may also be used depending on theavailable power supply and controller. As noted above, the longer times(e.g., where the open circuit voltage is measured during the secondrelaxation) may be beneficial in that they still provide useful opencircuit voltage information without the need for high end equipmentcapable of operating precisely at very short timeframes.

In certain implementations, the open circuit voltage ismeasured/recorded after a timeframe that is dependent upon the behaviorof the open circuit voltage. In other words, the open circuit voltagemay be measured over time after open circuit conditions are applied, andthe voltage chosen for analysis may be selected based on the voltage vs.time behavior. As described above, after application of open circuitconditions, the voltage goes through an initial drop, followed by afirst relaxation, a first plateau, and a second relaxation. Each ofthese periods may be identified on a voltage vs. time plot based on theslope of curve. For example, the first plateau region will relate to aportion of the plot where the magnitude of dV_(oc)/dt is relatively low.This may correspond to conditions in which the ionic current has stopped(or nearly stopped) decaying. As such, in certain embodiments, the opencircuit voltage used in the feedback/analysis is the voltage measured ata time when the magnitude of dV_(oc)/dt drops below a certain threshold.

Returning to FIG. 7B, after the open circuit voltage response ismeasured, it can be compared to a target open circuit voltage atoperation 751. The target open circuit voltage may correspond to thehold voltage. In certain cases, discussed further below, the target opencircuit voltage corresponds to the hold voltage as modified by anoffset. Techniques for choosing an appropriate offset from the holdvoltage are discussed further below. Where the open circuit voltageresponse indicates that the optical transition is not yet nearlycomplete (i.e., where the open circuit voltage has not yet reached thetarget open circuit voltage), the method continues at operation 753,where the applied voltage is increased to the drive voltage for anadditional period of time. After the additional period of time haselapsed, the method can repeat from operation 747, where the opencircuit conditions are again applied to the device. At some point in themethod 741, it will be determined in operation 751 that the open circuitvoltage response indicates that the optical transition is nearlycomplete (i.e., where the open circuit voltage response has reached thetarget open circuit voltage). When this is the case, the methodcontinues at operation 755, where the applied voltage is maintained atthe hold voltage for the duration of the ending optical state.

The method 741 of FIG. 7B is very similar to the method 701 of FIG. 7A.The main difference is that in FIG. 7B, the relevant variable measuredis the open circuit voltage, while in FIG. 7A, the relevant variablemeasured is the current response when a reduced voltage is applied. Inanother embodiment, discussed further below in the section regardingControlling an Optical Transition using Electrical Feedback toTransition Within a Desired Timeframe, the method 921 of FIG. 9A ismodified in the same way. In other words, the method 921 may be alteredsuch that probing occurs by placing the device in open circuitconditions and measuring the open circuit voltage rather than a currentresponse.

In another embodiment, the process for monitoring and controlling anoptical transition takes into account the total amount of chargedelivered to the electrochromic device during the transition, per unitarea of the device. This quantity may be referred to as the deliveredcharge density or total delivered charge density. As such, an additionalcriterion such as the total charge density delivered may be used toensure that the device fully transitions under all conditions.

The total delivered charge density may be compared to a threshold chargedensity (also referred to as a target charge density) to determinewhether the optical transition is nearly complete. The threshold chargedensity may be chosen based on the minimum charge density required tofully complete or nearly complete the optical transition under thelikely operating conditions. In various cases, the threshold chargedensity may be chosen/estimated based on the charge density required tofully complete or nearly complete the optical transition at a definedtemperature (e.g., at about −40° C., at about −30° C., at about −20° C.,at about −10° C., at about 0° C., at about 10° C., at about 20° C., atabout 25° C., at about 30° C., at about 40° C., at about 60° C., etc.).

The optimum threshold charge density may also be affected by the leakagecurrent of the electrochromic device. Devices that have higher leakagecurrents should have higher threshold charge densities. In someembodiments, an appropriate threshold charge density may be determinedempirically for an individual window or window design. In other cases,an appropriate threshold may be calculated/selected based on thecharacteristics of the window such as the size, bus bar separationdistance, leakage current, starting and ending optical states, etc.Example threshold charge densities range between about 1×10⁻⁵ C/cm² andabout 5 C/cm², for example between about 1×10⁻⁴ and about 0.5 C/cm², orbetween about 0.005-0.05 C/cm², or between about 0.01-0.04 C/cm², orbetween about 0.01-0.02 in many cases. Smaller threshold chargedensities may be used for partial transitions (e.g., fully clear to 25%tinted) and larger threshold charge densities may be used for fulltransitions. A first threshold charge density may be used forbleaching/clearing transitions, and a second threshold charge densitymay be used for coloring/tinting transitions. In certain embodiments,the threshold charge density is higher for tinting transitions than forclearing transitions. In a particular example, the threshold chargedensity for tinting is between about 0.013-0.017 C/cm², and thethreshold charge density for clearing is between about 0.016-0.020C/cm². Additional threshold charge densities may be appropriate wherethe window is capable of transitioning between more than two states. Forinstance, if the device switches between four different optical states:A, B, C, and D, a different threshold charge density may be used foreach transition (e.g., A to B, A to C, A to D, B to A, etc.).

In some embodiments, the threshold charge density is determinedempirically. For instance, the amount of charge required to accomplish aparticular transition between desired end states may be characterizedfor devices of different sizes. A curve may be fit for each transitionto correlate the bus bar separation distance with the required chargedensity. Such information may be used to determine the minimum thresholdcharge density required for a particular transition on a given window.In some cases, the information gathered in such empirical determinationsis used to calculate an amount of charge density that corresponds to acertain level of change (increase or decrease) in optical density.

FIG. 7C presents a flow chart for a method 761 for monitoring andcontrolling an optical transition in an electrochromic device. Themethod starts at operations 763 and 765, which correspond to operations703 and 705 of FIG. 7A. At 763, the controller or other appropriatelogic receives instructions to undergo an optical transition. Then, atoperation 765, the controller applies a drive voltage to the bus bars.After allowing the optical transition to proceed incrementally, themagnitude of the voltage applied to the bus bars is reduced to a probevoltage (which in some cases is the hold voltage, and in other cases isthe hold voltage modified by an offset) at operation 767. Next atoperation 769, the current response to the reduced applied voltage ismeasured.

Thus far, the method 761 of FIG. 7C is identical to the method 701 ofFIG. 7A. However, the two methods diverge at this point in the process,with method 761 continuing at operation 770, where the total deliveredcharge density is determined. The total delivered charge density may becalculated based on the current delivered to the device during theoptical transition, integrated over time. At operation 771, the relevantcontroller logic may determine whether the current response and totaldelivered charge density each indicate that the optical transition isnearly complete. As explained above, the determination of whether anoptical transition is nearly complete can be accomplished in variousways. For example, it may be determined by the current reaching aparticular threshold, and by the delivered charge density reaching aparticular threshold. Both the current response and the total deliveredcharge density must indicate that the transition is nearly completebefore the method can continue on at operation 775, where the appliedvoltage is transitioned to or maintained at the hold voltage for theduration of the ending optical state. Assuming at least one of thecurrent response and total delivered charge density indicate that theoptical transition is not yet nearly complete at operation 771, processcontrol is directed to an operation denoted by reference number 773. Inthis operation, the applied voltage is returned to the magnitude of thedrive voltage. Process control then loops back to operation 767 wherethe optical transition is allowed to proceed by a further incrementbefore again dropping the magnitude of the applied voltage to the busbars.

FIG. 7D presents an alternative method for monitoring and controlling anoptical transition in an electrochromic device. The method starts atoperations 783 and 785, which correspond to operations 703 and 705 ofFIG. 7A. At 783, the controller or other appropriate logic receivesinstructions to undergo an optical transition. Then, at operation 785,the controller applies a drive voltage to the bus bars. After allowingthe optical transition to proceed incrementally, open circuit conditionsare applied to the device at operation 787. Next at operation 789, theopen circuit voltage of the device is measured.

Thus far, the method 781 of FIG. 7D is identical to the method 741 ofFIG. 7B. However, the two methods diverge at this point in the process,with method 781 continuing at operation 790, where the total deliveredcharge density is determined. The total delivered charge density may becalculated based on the current delivered to the device during theoptical transition, integrated over time. At operation 791, the relevantcontroller logic may determine whether the open circuit voltage andtotal delivered charge density each indicate that the optical transitionis nearly complete. Both the open circuit voltage response and the totaldelivered charge density must indicate that the transition is nearlycomplete before the method can continue on at operation 795, where theapplied voltage is transitioned to or maintained at the hold voltage forthe duration of the ending optical state. Assuming at least one of theopen circuit voltage response and total delivered charge densityindicate that the optical transition is not yet nearly complete atoperation 791, process control is directed to an operation denoted byreference number 793. In this operation, the applied voltage is returnedto the magnitude of the drive voltage. Process control then loops backto operation 787 where the optical transition is allowed to proceed by afurther increment before again applying open circuit conditions to thedevice. The method 781 of FIG. 7D is very similar to the method 761 ofFIG. 7C. The principal difference between the two embodiments is that inFIG. 7C, the applied voltage drops and a current response is measured,whereas in FIG. 7D, open circuit conditions are applied and an opencircuit voltage is measured.

In certain implementations, the method involves using a static offset tothe hold voltage. This offset hold voltage may be used to probe thedevice and elicit a current response, as described in relation to FIGS.7A and 7C, for instance. The offset hold voltage may also be used as atarget open circuit voltage, as described in relation to FIGS. 7B and7D. In certain cases, particularly for windows with a large separationbetween the bus bars (e.g., at least about 25″), the offset can bebeneficial in ensuring that the optical transition proceeds tocompletion across the entire window.

In many cases, an appropriate offset is between about 0-0.5 V (e.g.,about 0.1-0.4 V, or between about 0.1-0.2 V). Typically, the magnitudeof an appropriate offset increases with the size of the window. Anoffset of about 0.2 V may be appropriate for a window of about 14inches, and an offset of about 0.4 V may be appropriate for a window ofabout 60 inches. These values are merely examples and are not intendedto be limiting. In some embodiments, a window controller is programmedto use a static offset to V_(hold). The magnitude and in some casesdirection of the static offset may be based on the devicecharacteristics such as the size of the device and the distance betweenthe bus bars, the driving voltage used for a particular transition, theleakage current of the device, the peak current density, capacitance ofthe device, etc. In various embodiments, the static offset is determinedempirically. In some designs, it is calculated dynamically, when thedevice is installed or while it is installed and operating, frommonitored electrical and/or optical parameters or other feedback.

In other embodiments, a window controller may be programmed todynamically calculate the offset to V_(hold). In one implementation, thewindow controller dynamically calculates the offset to V_(hold) based onone or more of the device's current optical state (OD), the currentdelivered to the device (I), the rate of change of current delivered tothe device (dl/dt), the open circuit voltage of the device (V_(oc)), andthe rate of change of the open circuit voltage of the device(dV_(oc)/dt). This embodiment is particularly useful because it does notrequire any additional sensors for controlling the transition. Instead,all of the feedback is generated by pulsing the electronic conditionsand measuring the electronic response of the device. The feedback, alongwith the device characteristics mentioned above, may be used tocalculate the optimal offset for the particular transition occurring atthat time. In other embodiments, the window controller may dynamicallycalculate the offset to V_(hold) based on certain additional parameters.These additional parameters may include the temperature of the device,ambient temperature, and signals gathered by photoptic sensors on thewindow. These additional parameters may be helpful in achieving uniformoptical transitions at different conditions. However, use of theseadditional parameters also increases the cost of manufacture due to theadditional sensors required.

The offset may be beneficial in various cases due to the non-uniformquality of the effective voltage, V_(eff), applied across the device.The non-uniform V_(eff) is shown in FIG. 4C, for example, describedabove. Because of this non-uniformity, the optical transition does notoccur in a uniform manner. In particular, areas near the bus barsexperience the greatest V_(eff) and transition quickly, while areasremoved from the bus bars (e.g., the center of the window) experiencethe lowest V_(eff) and transition more slowly. The offset can helpensure that the optical transition proceeds to completion at the centerof the device where the change is slowest.

FIGS. 8A and 8B show graphs depicting the total charge delivered overtime and the applied voltage over time during two differentelectrochromic tinting transitions. The window in each case measuredabout 24×24 inches. The total charge delivered is referred to as theTint Charge Count, and is measured in coulombs (C). The total chargedelivered is presented on the left hand y-axis of each graph, and theapplied voltage is presented on the right hand y-axis of each graph. Ineach figure, line 802 corresponds to the total charge delivered and line804 corresponds to the applied voltage. Further, line 806 in each graphcorresponds to a threshold charge (the threshold charge densitymultiplied by the area of the window), and line 808 corresponds to atarget open circuit voltage. The threshold charge and target opencircuit voltage are used in the method shown in FIG. 7D tomonitor/control the optical transition.

The voltage curves 804 in FIGS. 8A and 8B each start out with a ramp todrive component, where the magnitude of the voltage ramps up to thedrive voltage of about −2.5V. After an initial period of applying thedrive voltage, the voltage begins to spike upwards at regular intervals.These voltage spikes occur when the electrochromic device is beingprobed. As described in FIG. 7D, the probing occurs by applying opencircuit conditions to the device. The open circuit conditions result inan open circuit voltage, which correspond to the voltage spikes seen inthe graphs. Between each probe/open circuit voltage, there is anadditional period where the applied voltage is the drive voltage. Inother words, the electrochromic device is driving the transition andperiodically probing the device to test the open circuit voltage andthereby monitor the transition. The target open circuit voltage,represented by line 808, was selected to be about −1.4V for each case.The hold voltage in each case was about −1.2V. Thus, the target opencircuit voltage was offset from the hold voltage by about 0.2V.

In the transition of FIG. 8A, the magnitude of the open circuit voltageexceeds the magnitude of the target open circuit voltage at about 1500seconds. Because the relevant voltages in this example are negative,this is shown in the graph as the point at which the open circuitvoltage spikes first fall below the target open circuit voltage. In thetransition of FIG. 8B, the magnitude of the open circuit voltage exceedsthe magnitude of the target open circuit voltage sooner than in FIG. 8A,around 1250 seconds.

The total delivered charge count curves 802 in FIGS. 8A and 8B eachstart at 0 and rise monotonically. In the transition of FIG. 8A, thedelivered charge reaches the threshold charge at around 1500 seconds,which was very close to the time at which the target open circuitvoltage was met. Once both conditions were met, the voltage switchedfrom the drive voltage to the hold voltage, around 1500 seconds. In thetransition of FIG. 8B, the total delivered charge took about 2100seconds to reach the charge threshold, which is about 14 minutes longerthan it took the voltage to reach the target voltage for thistransition. After both the target voltage and threshold charge are met,the voltage is switched to the hold voltage. The additional requirementof the total charge delivered results in the FIG. 8B case driving thetransition at the drive voltage for a longer time than might otherwisebe used. This helps ensure full and uniform transitions across manywindow designs at various environmental conditions.

In another embodiment, the optical transition is monitored throughvoltage sensing pads positioned directly on the transparent conductivelayers (TCLs). This allows for a direct measurement of the V_(eff) atthe center of the device, between the bus bars where V_(eff) is at aminimum. In this case, the controller indicates that the opticaltransition is complete when the measured V_(eff) at the center of thedevice reaches a target voltage such as the hold voltage. In variousembodiments, the use of sensors may reduce or eliminate the benefit fromusing a target voltage that is offset from the hold voltage. In otherwords, the offset may not be needed and the target voltage may equal thehold voltage when the sensors are present. Where voltage sensors areused, there should be at least one sensor on each TCL. The voltagesensors may be placed at a distance mid-way between the bus bars,typically off to a side of the device (near an edge) so that they do notaffect (or minimally affect) the viewing area. The voltage sensors maybe hidden from view in some cases by placing them proximate aspacer/separator and/or frame that obscures the view of the sensor.

FIG. 8C presents an embodiment of an EC window 890 that utilizes sensorsto directly measure the effective voltage at the center of the device.The EC window 890 includes top bus bar 891 and bottom bus bar 892, whichare connected by wires 893 to a controller (not shown). Voltage sensor896 is placed on the top TCL, and voltage sensor 897 is placed on thebottom TCL. The sensors 896 and 897 are placed at a distance mid-waybetween the bus bars 891 and 892, though they are off to the side of thedevice. In some cases the voltage sensors may be positioned such thatthey reside within a frame of the window. This placement helps hide thesensors and promote optimal viewing conditions. The voltage sensors 896and 897 are connected to the controller through wires 898. The wires 893and 898 may pass under or through a spacer/separator placed and sealedin between the panes (also referred to as lites) of the window. Thewindow 890 shown in FIG. 8C may utilize any of the methods describedherein for controlling an optical transition.

In some implementations, the voltage sensing pads may be conductive tapepads. The pads may be as small as about 1 mm² in some embodiments. Inthese or other cases, the pads may be about 10 mm² or less. A four wiresystem may be used in embodiments utilizing such voltage sensing pads.

Controlling a Transition Using Electrical Feedback to Transition withina Desired Timeframe

Separately, in some implementations, the method or controller mayspecify a total duration of the transition. In such implementations, thecontroller may be programmed to use a modified probing algorithm tomonitor the progress of the transition from the starting state to theend state. The progress can be monitored by periodically reading acurrent value in response to a drop in the applied voltage magnitudesuch as with the probing technique described above. The probingtechnique may also be implemented using a drop in applied current (e.g.,measuring the open circuit voltage). The current or voltage responseindicates how close to completion the optical transition has come. Insome cases, the response is compared to a threshold current or voltagefor a particular time (e.g., the time that has elapsed since the opticaltransition was initiated). In some embodiments, the comparison is madefor a progression of the current or voltage responses using sequentialpulses or checks. The steepness of the progression may indicate when theend state is likely to be reached. A linear extension to this thresholdcurrent may be used to predict when the transition will be complete, ormore precisely when it will be sufficiently complete that it isappropriate to drop the drive voltage to the hold voltage.

With regard to algorithms for ensuring that the optical transition fromfirst state to the second state occurs within a defined timeframe, thecontroller may be configured or designed to increase the drive voltageas appropriate to speed up the transition when the interpretation of thepulse responses suggests that the transition is not progressing fastenough to meet the desired speed of transition. In certain embodiments,when it is determined that the transition is not progressingsufficiently fast, the transition switches to a mode where it is drivenby an applied current. The current is sufficiently great to increase thespeed of the transition but is not so great that it degrades or damagesthe electrochromic device. In some implementations, the maximum suitablysafe current may be referred to as I_(safe). Examples of I_(safe) mayrange between about 5 and 250 μA/cm². In current controlled drive mode,the applied voltage is allowed to float during the optical transition.Then, during this current controlled drive step, could the controllerperiodically probes by, e.g., dropping to the hold voltage and checkingfor completeness of transition in the same way as when using a constantdrive voltage.

In general, the probing technique may determine whether the opticaltransition is progressing as expected. If the technique determines thatthe optical transition is proceeding too slowly, it can take steps tospeed the transition. For example, it can increase the drive voltage.Similarly, the technique may determine that the optical transition isproceeding too quickly and risks damaging the device. When suchdetermination is made, the probing technique may take steps to slow thetransition. As an example, the controller may reduce the drive voltage.

In some applications, groups of windows are set to matching transitionrates by adjusting the voltage and/or driving current based on thefeedback obtained during the probing (by pulse or open circuitmeasurements). In embodiments where the transition is controlled bymonitoring the current response, the magnitude of the current responsemay be compared from controller to controller (for each of the group ofwindows) to determine how to scale the driving potential or drivingcurrent for each window in the group. The rate of change of open circuitvoltage could be used in the same manner.

FIG. 9A presents a flowchart 921 depicting an example process forensuring that the optical transition occurs sufficiently fast, e.g.,within a defined time period. The first four depicted operations inflowchart 921 correspond to the first four operations in flowchart 701.In other words, operation 923, 925, 927, and 929 of flowchart 921correspond to operations 703, 705, 707, and 709 of flowchart 701 fromFIG. 7A. Briefly, in operation 923, the controller or other appropriatelogic receives instructions to undergo an optical transition. Then, atoperation 925, the controller applies a drive voltage to the bus bars.After allowing the optical transition to proceed incrementally, thecontroller drops the magnitude of the applied voltage to the bus bars.See operation 927. The magnitude of the lower voltage is typically,though not necessarily, the hold voltage. As mentioned, the lowervoltage may also be the hold voltage as modified by an offset (theoffset often falling between about 0-1V, for example between about0-0.4V in many cases). Next, the controller measures the currentresponse to the applied voltage drop. See operation 929.

The controller next determines whether the current response indicatesthat the optical transition is proceeding too slowly. See decision 931.As explained, the current response may be analyzed in various waysdetermine whether the transition is proceeding with sufficient speed.For example, the magnitude of the current response may be considered orthe progression of multiple current responses to multiple voltage pulsesmay be analyzed to make this determination.

Assuming that operation 931 establishes that the optical transition isproceeding rapidly enough, the controller then increases the appliedvoltage back to the drive voltage. See operation 933. Thereafter, thecontroller then determines whether the optical transition issufficiently complete that further progress checks are unnecessary. Seeoperation 935. In certain embodiments, the determination in operation935 is made by considering the magnitude of the current response asdiscussed in the context of FIG. 7A. Assuming that the opticaltransition is not yet sufficiently complete, process control returns tooperation 927, where the controller allows the optical transition toprogress incrementally further before again dropping the magnitude ofthe applied voltage.

Assuming that execution of operation 931 indicates that the opticaltransition is proceeding too slowly, process control is directed to anoperation 937 where the controller increases the magnitude of theapplied voltage to a level that is greater than the drive voltage. Thisover drives the transition and hopefully speeds it along to a level thatmeets specifications. After increasing the applied voltage to thislevel, process control is directed to operation 927 where the opticaltransition continues for a further increment before the magnitude of theapplied voltage is dropped. The overall process then continues throughoperation 929, 931, etc. as described above. At some point, decision 935is answered in the affirmative and the process is complete. In otherwords, no further progress checks are required. The optical transitionthen completes as illustrated in, for example, flowchart 701 of FIG. 7A.

In certain embodiments, the method 921 may be altered such that probingoccurs by placing the device in open circuit conditions and measuringthe open circuit voltage rather than measuring a current response. Insome embodiments, the method 921 may be modified by including anadditional charge counting and comparison step, as presented inoperations 770/771 of FIG. 7C and operations 790/791 of FIG. 7D.

Controlling a Transition Using Electrical Feedback to Transition to aModified End State

Another application of the probing techniques disclosed herein involveson-the-fly modification of the optical transition to a different endstate. In some cases, it will be necessary to change the end state aftera transition begins. Examples of reasons for such modification include auser's manual override a previously specified end tint state and a widespread electrical power shortage or disruption. In such situations, theinitially set end state might be transmissivity=40% and the modified endstate might be transmissivity=5%.

Where an end state modification occurs during an optical transition, theprobing techniques disclosed herein can adapt and move directly to thenew end state, rather than first completing the transition to theinitial end state.

In some implementations, the transition controller/method detects thecurrent state of the window using a voltage/current sense as disclosedherein and then moves to a new drive voltage immediately. The new drivevoltage may be determined based on the new end state and optionally thetime allotted to complete the transition. If necessary, the drivevoltage is increased significantly to speed the transition or drive agreater transition in optical state. The appropriate modification isaccomplished without waiting for the initially defined transition tocomplete. The probing techniques disclosed herein provide a way todetect where in the transition the device is and make adjustments fromthere.

FIG. 9B illustrates a flowchart for a method 908 for controlling anoptical transition in an electrochromic device. The method 908 of FIG.9B is similar to the method 781 of FIG. 7D in that both methods involvemeasuring an open circuit voltage and charge count, which are used asfeedback to control the transition. The method 908 begins at operation910 where the controller is turned on. Next, at operation 912, the opencircuit voltage (Von) is read and the device waits for an initialcommand. An initial command is received at operation 914, the commandindicating that the window should switch to a different optical state.After the command is received, open circuit conditions are applied andthe open circuit voltage is measured at operation 916. The amount ofcharge delivered (Q) may also be read at block 916. These parametersdetermine the direction of the transition (whether the window issupposed to get more tinted or more clear), and impact the optimal driveparameter. An appropriate drive parameter (e.g., drive voltage) isselected at operation 916. This operation may also involve revising thetarget charge count and target open circuit voltage, particularly incases where an interrupt command is received, as discussed furtherbelow.

After the open circuit voltage is read at operation 916, theelectrochromic device is driven for a period of time. The drive durationmay be based on the busbar separation distance in some cases. In othercases, a fixed drive duration may be used, for example about 30 seconds.This driving operation may involve applying a drive voltage or currentto the device. Operation 918 may also involve modifying a driveparameter based on the sensed open circuit voltage and/or charge count.Next, at operation 920, it is determined whether the total time of thetransition (thus far) is less than a threshold time. The threshold timeindicated in FIG. 9B is 2 hours, though other time periods may be usedas appropriate. If it is determined that the total time of transition isnot less than the threshold time (e.g., where the transition has takenat least 2 hours and is not yet complete), the controller may indicatethat it is in a fault state at operation 930. This may indicate thatsomething has caused an error in the transition process. Otherwise,where the total time of transition is determined to be less than thethreshold time, the method continues at operation 922. Here, opencircuit conditions are again applied, and the open circuit voltage ismeasured. At operation 924, it is determined whether the measured opencircuit voltage is greater than or equal to the target voltage (in termsof magnitude). If so, the method continues at operation 926, where it isdetermined whether the charge count (Q) is greater than or equal to thetarget charge count. If the answer in either of operations 924 or 926 isno, the method returns to block 918 where the electrochromic devicetransition is driven for an additional drive duration. Where the answerin both of operations 924 and 926 is yes, the method continues atoperation 928, where a hold voltage is applied to maintain theelectrochromic device in the desired tint state. Typically, the holdvoltage continues to be applied until a new command is received, oruntil a timeout is experienced.

When a new command is received after the transition is complete, themethod may return to operation 916. Another event that can cause themethod to return to operation 916 is receiving an interrupt command, asindicated in operation 932. An interrupt command may be received at anypoint in the method after an initial command is received at operation914 and before the transition is essentially complete at operation 928.The controller should be capable of receiving multiple interruptcommands over a transition. One example interrupt command involves auser directing a window to change from a first tint state (e.g., fullyclear) to a second tint state (e.g., fully tinted), then interruptingthe transition before the second tint state is reached to direct thewindow to change to a third tint state (e.g., half tinted) instead ofthe second tint state. After receiving a new command or an interruptcommand, the method returns to block 916 as indicated above. Here, opencircuit conditions are applied and the open circuit voltage and chargecount are read. Based on the open circuit voltage and charge countreadings, as well as the desired third/final tint state, the controlleris able to determine appropriate drive conditions (e.g., drive voltage,target voltage, target charge count, etc.) for reaching the third tintstate. For instance, the open circuit voltage/charge count may be usedto indicate in which direction the transition should occur. The chargecount and charge target may also be reset after receiving a new commandor an interrupt command. The updated charge count may relate to thecharge delivered to move from the tint state when the new/interruptcommand is received to the desired third tint state. Because the newcommand/interrupt command will change the starting and ending points ofthe transition, the target open circuit voltage and target charge countmay need to be revised. This is indicated as an optional part ofoperation 916, and is particularly relevant where a new or interruptcommand is received.

In a related embodiment, the method 908 may be altered such that probingoccurs by dropping the magnitude of the applied voltage and measuring acurrent response, rather than applying open circuit conditions andmeasuring an open circuit voltage in operations 922 and 924. In anotherrelated embodiment, the method 908 may be altered such that probing doesnot involve reading a charge count (e.g., operation 926 is omitted) orusing such charge count as feedback. In these embodiments, probing mayinvolve either measuring a current response after an applied voltage isreduced, or measuring an open circuit voltage after open circuitconditions are applied.

It should be understood that the probing techniques presented in any ofthe various sections herein need not be limited to measuring themagnitude of the device's current in response to a voltage drop (pulse).There are various alternatives to measuring the magnitude of the currentresponse to a voltage pulse as an indicator of how far as the opticaltransition has progressed. In one example, the profile of a currenttransient provides useful information. In another example, measuring theopen circuit voltage of the device may provide the requisiteinformation. In such embodiments, the pulse involves simply applying novoltage to device and then measuring the voltage that the open circuitdevice applies. Further, it should be understood that current andvoltage based algorithms are equivalent. In a current based algorithm,the probe is implemented by dropping the applied current and monitoringthe device response. The response may be a measured change in voltage.For example, the device may be held in an open circuit condition tomeasure the voltage between bus bars.

Controlling Transitions Using Electrical Feedback to Transition aPlurality of Windows to Matching Tint Levels/Rates

In some applications, groups of windows are set to matching transitionrates by adjusting the voltage and/or driving current based on thefeedback obtained during probing, such probing techniques beingdescribed above (e.g., probing may involve measurement of an opencircuit voltage after open circuit conditions are applied, or it mayinvolve measurement of a current response after application of a voltagepulse, and in some cases it may involve measurement of a deliveredcharge in addition to measuring either a voltage or current response).FIG. 9C presents a flowchart of one such embodiment. The method 950begins at operation 951, where one or more controllers receiveinstructions to undergo an optical transition on multiple windowssimultaneously. At operation 953, drive conditions (e.g., drive currentand/or drive voltage) are applied to the bus bars on each window. Thedrive conditions may be initially equal or unequal between the differentwindows. Unequal drive conditions may be particularly useful where thewindows are known to have different switching properties, for instancewhere the windows are of different sizes. Next, at operation 955, afterallowing the optical transition on each window to proceed incrementally,each window is electronically probed. Probing may occur through any ofthe methods described herein (e.g., pulsing current, pulsing voltage,counting charge, and combinations thereof). After probing, theelectronic response from each window is measured and compared atoperation 957. The electronic responses may simply be compared againstone another. Alternatively or in addition, the electronic responses canbe evaluated to determine whether the responses indicate that eachtransition will occur within a target timeframe.

In embodiments where the transition is controlled by monitoring thecurrent response, the magnitude of the current response may be comparedfrom controller to controller (for each window in the group of windows)to determine how to scale the driving potential or driving current foreach window in the group. The rate of change of open circuit voltagecould be used in the same manner. By scaling the driving potential ordriving current for each window based on the feedback response, theamount and/or rate of tinting may be controlled to be uniform betweenall of the windows. This scaling of the drive conditions is described inblocks 959, 961, 962, and 963. The drive conditions for each window canbe continuously and individually monitored and updated based on thefeedback responses for each window, as shown by the various loops inFIG. 9C. Once the optical transitions are complete (evaluated atoperation 965), the windows are all transitioned to their final endstates and the method is complete.

Any group of windows may be controlled together in this manner. Forinstance, two or more adjacent windows can be controlled together. Inanother example, two or more windows (e.g., all windows) in a singleroom are controlled together. In another example, two or more windows(e.g., all windows) on a floor of a building are controlled together. Inyet another example, two or more windows (e.g., all windows) of abuilding are controlled together. In a further example, a number ofwindows are provided together in a curtain wall, and each window in thecurtain wall can be controlled together. An example of a folding curtainwall is shown in FIG. 10, described below.

FIG. 10 presents an example of a folding curtain wall 1003. The foldingcurtain wall 1003 includes four electrochromic windows 1000 a-d, whichare connected through a series of ribbon connectors 1005. Another ribbonconnector 1005 (or other connector) links the curtain wall 1003 to amaster controller 1010. Ribbon connectors are particularly useful forfolding curtain walls, as they can accommodate movement of the differentpanels. In a similar embodiment, a fixed curtain wall is used. Anyappropriate electrical connection may be used to connect the variouswindows in this case, as there is less concern with wires becomingpinched since the windows are static. Certain embodiments relate toensuring that the tint level of adjacent EC windows substantiallymatches, e.g., based on non-optical feedback control. Returning to theembodiment of FIG. 10, the master controller 1010 can control each ofthe windows 1000 a-d, either individually or as a group. In certainembodiments, the windows in the folding curtain wall 1003 may becontrolled as described to achieve substantially similar tint levels ineach of the windows 1000 a-d. For instance, a user may send a command tocause all of the windows to tint at the same level. In response, thecontroller 1010 (or multiple controllers, one for each window (notshown)) may probe the windows to determine their relative or absolutetint values. The response from each window can be compared, and theneach window can be individually driven based on the feedback responsefrom the probing to match the tint levels on each of the windows 1000a-d. Similarly, probing can be done during a transition to ensure thateach of the windows 1000 a-d is tinting at substantially the same rate.

Issues related to transitions involving multiple windows can beespecially problematic in certain contexts, for instance where thewindows exhibit different switching speeds due to differences in windowsize and/or other window characteristics (e.g., lithium ion mobility,TCO resistivity differences, replacement windows having differentcharacteristic than the windows in the original set, etc.). If a largerwindow is positioned next to a smaller window and the same drivingconditions are used to transition both windows, the smaller window willtypically transition faster than the neighboring larger window. This maybe aesthetically undesirable to occupants. As such, electrical feedbackcan be used to ensure that the various windows tint at the same rate orat rates that mask or otherwise minimize discernable opticaldifferences.

In some embodiments, a uniform tinting rate is achieved across multiplewindows by designating a desired transition time that is applicable tothe multiple windows. The individual windows can then be controlled(e.g., through a local window controller and/or a network controller)such that they each tint at a rate that will achieve the transitionduring the desired transition time. In the context of FIG. 9C, forexample, blocks 959 and 962 may be evaluated by analyzing the electricalresponses from each window to determine if each window will transitionwithin a desired transition time. In some embodiments, the desiredtransition time is either (a) programmed into or (b) dynamicallycalculated by one or more window or network controllers. Methods forachieving such control are described further above, particularly in thesection related to Controlling a Transition using Electrical Feedback toTransition Within a Desired Timeframe. Briefly, if the feedback responseindicates that the transition of a particular window is occurring tooslowly (such that the window will not transition within the desiredtimeframe), the drive conditions can be altered to increase the rate oftransition (e.g., a drive voltage applied to an overly slow window canbe increased). Similarly, in various embodiments, if the feedbackresponse indicates that the transition is occurring too quickly (suchthat the window will transition faster than the desired transitiontime), the drive conditions can be altered to decrease the rate oftransition for that window (e.g., a drive voltage applied to an overlyfast switching window can be reduced). The end result being, e.g., thateven for multiple windows in a façade, the façade as a whole transitionsuniformly from the end user's perspective and, once in the desired tintstate, the group of adjacent windows appears uniformly tinted.

Where multiple windows are controlled in this manner, it may bedesirable for one or more controllers (e.g., window controllers and/or anetwork controller) to verify that the windows involved in thetransition are capable of transitioning within the desired transitiontime. For instance, if a smaller window can transition in 5 minutes buta larger adjacent window takes 15 minutes to transition, the desiredtransition time for both windows should be about 15 minutes or greater.

In one example, a desired transition time is programmed into individualwindows (e.g., into a pigtail, window controller, or other componenthaving localized memory). Each of the windows may have the sametransition time programmed in, such that they transition at the samerate. A window and/or network controller can then read the desiredtransition time information and verify that the window can be switchedwithin the desired transition time. Such verification may occur beforethe transition begins. In other cases the verification occurs during thetransition. If any of the windows in the group are not able totransition within the desired transition time, a new target transitiontime may be designated based on the slowest switching window (i.e., thelimiting window). The new target transition may be applied to all thewindows being controlled together in certain embodiments. The windowand/or network controller can dynamically adjust the driving conditions,for example based on feedback as described above, to ensure that each ofthe windows transitions at a desired rate and within the desiredtransition time.

In a similar example, a group of windows may be zoned together such thatthey transition together as a group. The grouping of the windows may bepre-programmed, or it may be designated on-the-fly (e.g., immediatelybefore a transition, or even during a transition). A network controller,or a group of window controllers working together, can then determinewhich window(s) in the group will be the slowest transitioning windows.Typically the largest windows are those that transition the slowest. Thedesired transition time can then be set based on the slowest (generallylargest) window. In such embodiments, the individual windows may beprogrammed to designate their size (e.g., in a pigtail, windowcontroller, or other component having memory). It is not necessary todesignate a particular switching time for each window. A networkcontroller, for instance having a microprocessor unit, can be used todefine a control algorithm for each individual window after the windowsare grouped together. The network controller may select a desiredtransition time (for all windows in the group) based on the time ittakes to transition the slowest (generally largest) window in the group.The windows can then be individually controlled, based on feedback asdescribed above, such that they transition over the course of thedesired transition time.

As noted, the zoning of the windows can be designated on-the-fly. Thisfeature is beneficial because it helps provide a high degree offlexibility and responsiveness when controlling a number of windowstogether. In one example shown in method 970 of FIG. 9D, a first set ofwindows is defined and instructed to undergo an optical transition inoperation 971. The transition time is based on the slowest changingwindow in the first set of windows. Next, at operation 973, driveconditions are applied to each window to cause each window to transitionover the transition time. The method 970 may then proceed as describedin relation to method 950 of FIG. 9B. However, at some point during thetransition of the first set of windows, instructions may be received(e.g., from a user, controller, etc.) that a second set of windowsshould be transitioned instead of the first set of windows. As such,operation 985 is included to check for any instructions to modify thegroup of windows being switched. If no such instructions have beenreceived, the first set of windows continues to transition as normal.However, if instructions are received to define a second set of windowsto transition, the method continues at operation 986, where the driveconditions are updated and applied to the windows in the second set. Theupdated drive conditions are based on the windows that are included inthe second set of windows, including an updated transition time(sometimes referred to as a second transition time) based on the windowsin the second set. The second set of windows may be different from thefirst set of windows, though the two sets may include some overlappingwindows (e.g., certain windows may be included in both the first andsecond set of windows). A controller can then transition all the windowsin the second set together at matching tint levels or tint rates byfollowing the operations shown in method 970, with drive conditions andtransition time now being based on the windows in the second set ofwindows instead of the first set of windows.

One example where this may occur is when a user initially decides totransition two out of three electrochromic windows in a room, thenduring the transition decides to transition all three electrochromicwindows in the room. After designating all three windows as the secondset of windows, a controller may use feedback to control all threewindows together at matching tint levels and/or tint rates based on theslowest transitioning window in the second set of windows. Oneconsequence is that a window that is in both the first and second setsof windows may experience different drive conditions at different pointsin time due to the differing windows within the groups beingtransitioned together. For example, a later defined group of windows mayinclude a larger/slower transitioning window than an initially definedgroup of windows. As such, when the windows are grouped to include thelarge/slow window, the transition rate of all the other windows may beslower. The ending optical state for the second set of windows may bethe same or different from the ending optical state (or starting opticalstate) of the first set of windows.

In certain embodiments where multiple windows transition at the sametime, it may be desirable to enable both (a) fast-as-possibletransitions for each individual window under certain conditions, and (b)uniform transitions across the multiple windows under other conditions.For example, it may be desirable for regularly scheduled transitions tooccur uniformly for a group of windows. Uniformity may be beneficial inthis context because uniform transitions are less distracting, which isparticularly advantageous for scheduled transitions that may nototherwise draw an occupant's attention. In other words, it is beneficialfor scheduled transitions to occur more subtly. In contrast, it may bedesirable for non-scheduled, user-initiated transitions to occur asquickly as possible for each individual window. Fast, non-uniformtransitions may be beneficial in this context because users often likefast response times when they input a command. Where a user has input acommand to transition the windows, the potentially distracting nature ofa non-uniform transition is less problematic as the user has alreadydevoted some attention to the windows by initiating the command. In asimilar embodiment, a user who desires to switch a group of windows canchoose to do so either at a uniform rate across all the windows, or atdiffering (e.g., maximum) rates for each window.

As noted above, different windows can transition at different rates dueto differences in size as well as other window characteristics. Incertain embodiments, one or more controllers are configured to accountfor differences in switching speeds based on both of these concepts. Forinstance, one or more controllers may first designate an initial set ofinstructions used to transition the windows in the group based on thesize of each window. Then, one or more controllers may modify theindividual instructions for each window based on the individualtransition characteristics (e.g., lithium ion mobility, TCO resistivity,contact resistance at the busbars and/or electrical leads, windowtemperature, etc.) for each window.

Controllers for Electrochromic Devices

As indicated, the switchable optical device will have an associatedcontroller, e.g. a microprocessor that controls and manages the devicedepending on the input. It is designed or configured (e.g., programmed)to implement a control algorithm of the types described above. Invarious embodiments, the controller detects current and/or voltagelevels in the device and applies current and/or voltage as appropriate.The controller may also detect current and/or voltage levels to ensurethat the optical device stays within a safe voltage level and/or safecurrent level. The controller may also detect current, voltage, and/ordelivered charge levels in the device in order to determine anappropriate end point of a transition. In some cases the controller maydetect current, voltage, and/or delivered charge levels in the device inorder to ensure that a transition occurs within a desired timeframe. Insome cases the controller may detect current, voltage, and/or deliveredcharge levels in order to control a transition to a modified end state.In each of these examples, the controller uses an electrical response orother (often non-optical) characteristic of the device or transition asfeedback to control an ongoing transition. Further, the controller mayhave various additional features such as timers, charge detectors (e.g.,coulomb counters), oscillators, and the like.

In some embodiments, the controller is located external to the deviceand communicates with the device via a network. The communication can bedirect or indirect (e.g., via an intermediate node between a mastercontroller and the device). The communication may be made via wired or awireless connection. Various arrangements of external controllers arepresented in U.S. patent application Ser. No. 13/049,756, naming Brownet al. as inventors, titled “Multipurpose Controller for MultistateWindows” and filed on the same day as the present application, which isincorporated herein by reference in its entirety.

In some embodiment the controller is integrated with the optical deviceor housing. In a specific embodiment, the controller is integrated inthe housing or a seal of an insulated glass unit (IGU) containing aswitchable optical device. Various arrangements of integratedcontrollers are presented in U.S. Pat. No. 8,213,074, titled “OnboardController for Multistate Windows,” which is incorporated herein byreference in its entirety.

In one embodiment, the controller contains various components asdepicted in FIG. 11. As shown, a controller 1101 includes a powerconverter configured to convert a low voltage to the power requirementsof an EC device of an EC pane of an IGU. This power is typically fed tothe EC device via a driver circuit (power driver). In one embodiment,controller 1101 has a redundant power driver so that in the event onefails, there is a backup and the controller need not be replaced orrepaired.

Controller 1101 also includes a communication circuit (labeled“communication” in FIG. 11) for receiving and sending commands to andfrom a remote controller (depicted in FIG. 11 as “master controller”).The communication circuit also serves to receive and send input to andfrom a microcontroller. In one embodiment, the power lines are also usedto send and receive communications, for example, via protocols such asEthernet. The microcontroller includes a logic for controlling the atleast one EC pane based, at least in part, on input received from one ormore sensors. In this example sensors 1-3 are, for example, external tocontroller 1101, located for example in the window frame or proximatethe window frame. In one embodiment, the controller has at least one ormore internal sensors. For example, controller 1101 may also oralternatively have “onboard” sensors 4 and 5. In one embodiment, thecontroller uses the switchable optical device as a sensor, for example,by using current-voltage (I/V) data obtained from sending one or moreelectrical pulses through the EC device and analyzing the feedback.

In one embodiment, the controller includes a chip, a card or a boardwhich includes logic for performing one or more control functions. Powerand communication functions of controller 1101 may be combined in asingle chip, for example, a programmable logic device (PLD) chip, fieldprogrammable gate array (FPGA) and the like. Such integrated circuitscan combine logic, control and power functions in a single programmablechip. In one embodiment, where the electrochromic window (or IGU) hastwo electrochromic panes, the logic is configured to independentlycontrol each of the two electrochromic panes. In one embodiment, thefunction of each of the two electrochromic panes is controlled in asynergistic fashion, that is, so that each device is controlled in orderto complement the other. For example, the desired level of lighttransmission, thermal insulative effect, and/or other property arecontrolled via combination of states for each of the individual devices.For example, one electrochromic device may be placed in a tinted statewhile the other is used for resistive heating, for example, via atransparent electrode of the device. In another example, the opticalstates of the two electrochromic devices are controlled so that thecombined transmissivity is a desired outcome.

Controller 1101 may also have wireless capabilities, such as control andpowering functions. For example, wireless controls, such as Rf and/or IRcan be used as well as wireless communication such as Bluetooth, WiFi,Zigbee, EnOcean and the like to send instructions to the microcontrollerand for the microcontroller to send data out to, for example, otherwindow controllers and/or a building management system (BMS). Wirelesscommunication can be used in the window controller for at least one ofprogramming and/or operating the electrochromic window, collecting datafrom the electrochromic window from sensors as well as using theelectrochromic window as a relay point for wireless communication. Acontroller may include a wireless communication receiver and/ortransmitter for wireless communication. Data collected fromelectrochromic windows also may include count data such as number oftimes an electrochromic device has been activated (cycled), efficiencyof the electrochromic device over time, and the like.

Also, controller 1101 may have wireless power capability. That is,controller 1101 may have one or more wireless power receivers, thatreceive transmissions from one or more wireless power transmitters andthus controller 1101 can power the electrochromic window via wirelesspower transmission. Wireless power transmission includes, for examplebut not limited to, induction, resonance induction, radio frequencypower transfer, microwave power transfer and laser power transfer. Inone embodiment, power is transmitted to a receiver via radio frequency,and the receiver converts the power into electrical current utilizingpolarized waves, for example circularly polarized, ellipticallypolarized and/or dual polarized waves, and/or various frequencies andvectors. In another embodiment, power is wirelessly transferred viainductive coupling of magnetic fields. Exemplary wireless powerfunctions of electrochromic windows is described in U.S. patentapplication Ser. No. 12/971,576, filed Dec. 17, 2010, entitled “WirelessPowered Electrochromic Windows,” and naming Robert Rozbicki as inventor,which is incorporated by reference herein in its entirety.

Controller 1101 may also include an RFID tag and/or memory such as solidstate serial memory (e.g. I2C or SPI) which may optionally beprogrammable memory. Radio-frequency identification (RFID) involvesinterrogators (or readers), and tags (or labels). RFID tags usecommunication via electromagnetic waves to exchange data between aterminal and an object, for example, for the purpose of identificationand tracking of the object. Some RFID tags can be read from severalmeters away and beyond the line of sight of the reader.

RFID tags may contain at least two parts. One is an integrated circuitfor storing and processing information, modulating and demodulating aradio-frequency (Rf) signal, and other specialized functions. The otheris an antenna for receiving and transmitting the signal.

There are three types of RFID tags: passive RFID tags, which have nopower source and require an external electromagnetic field to initiate asignal transmission, active RFID tags, which contain a battery and cantransmit signals once a reader has been successfully identified, andbattery assisted passive (BAP) RFID tags, which require an externalsource to wake up but have significant higher forward link capabilityproviding greater range. RFID has many applications; for example, it isused in enterprise supply chain management to improve the efficiency ofinventory tracking and management.

In one embodiment, the RFID tag or other memory is programmed with atleast one of the following data: warranty information, installationinformation, vendor information, batch/inventory information, ECdevice/IGU characteristics, EC device cycling information and customerinformation. Examples of EC device and IGU characteristics include, forexample, window voltage (V_(W)), window current (I_(W)), EC coatingtemperature (T_(EC)), glass visible transmission (% T_(vis)), % tintcommand (external analog input from BMS), digital input states, andcontroller status. Each of these represents upstream information thatmay be provided from the controller. Examples of downstream data thatmay be provided to the controller include window drive configurationparameters, zone membership (e.g. what zone is this controller part of),% tint value, digital output states, and digital control (tint, clear,auto, reboot, etc.). Examples of window drive configuration parametersinclude clear to tinted transition ramp rate, clear to tinted transitionvoltage, initial tinting ramp rate, initial tinting voltage, initialtinting current limit, tinted hold voltage, tinted hold current limit,tinted to clear transition ramp rate, tinted to clear transitionvoltage, initial clearing ramp rate, initial clearing voltage, initialclearing current limit, clear hold voltage, clear hold current limit.

In one embodiment, a programmable memory is used in controllersdescribed herein. This programmable memory can be used in lieu of, or inconjunction with, RFID technology. Programmable memory has the advantageof increased flexibility for storing data related to the IGU to whichthe controller is matched.

FIG. 12 shows a cross-sectional axonometric view of an embodiment of anIGU 1202 that includes two window panes or lites 1216 and a controller1250. In various embodiments, IGU 1202 can include one, two, or moresubstantially transparent (e.g., at no applied voltage) lites 1216 aswell as a frame, 1218, that supports the lites 1216. For example, theIGU 1202 shown in FIG. 12 is configured as a double-pane window. One ormore of the lites 1216 can itself be a laminate structure of two, three,or more layers or lites (e.g., shatter-resistant glass similar toautomotive windshield glass). In IGU 1202, at least one of the lites1216 includes an electrochromic device or stack, 1220, disposed on atleast one of its inner surface, 1222, or outer surface, 1224: forexample, the inner surface 1222 of the outer lite 1216.

In multi-pane configurations, each adjacent set of lites 1216 can havean interior volume, 1226, disposed between them. Generally, each of thelites 1216 and the IGU 1202 as a whole are rectangular and form arectangular solid. However, in other embodiments other shapes (e.g.,circular, elliptical, triangular, curvilinear, convex, concave) may bedesired. In some embodiments, the volume 1226 between the lites 1216 isevacuated of air. In some embodiments, the IGU 1202 ishermetically-sealed. Additionally, the volume 1226 can be filled (to anappropriate pressure) with one or more gases, such as argon (Ar),krypton (Kr), or xenon (Xn), for example. Filling the volume 1226 with agas such as Ar, Kr, or Xn can reduce conductive heat transfer throughthe IGU 1202 because of the low thermal conductivity of these gases. Thelatter two gases also can impart improved acoustic insulation due totheir increased weight.

In some embodiments, frame 1218 is constructed of one or more pieces.For example, frame 1218 can be constructed of one or more materials suchas vinyl, PVC, aluminum (Al), steel, or fiberglass. The frame 1218 mayalso include or hold one or more foam or other material pieces that workin conjunction with frame 1218 to separate the lites 1216 and tohermetically seal the volume 1226 between the lites 1216. For example,in a typical IGU implementation, a spacer lies between adjacent lites1216 and forms a hermetic seal with the panes in conjunction with anadhesive sealant that can be deposited between them. This is termed theprimary seal, around which can be fabricated a secondary seal, typicallyof an additional adhesive sealant. In some such embodiments, frame 1218can be a separate structure that supports the IGU construct.

Each lite 1216 includes a substantially transparent or translucentsubstrate, 1228. Generally, substrate 1228 has a first (e.g., inner)surface 1222 and a second (e.g., outer) surface 1224 opposite the firstsurface 1222. In some embodiments, substrate 1228 can be a glasssubstrate. For example, substrate 1228 can be a conventional siliconoxide (SO_(x))-based glass substrate such as soda-lime glass or floatglass, composed of, for example, approximately 75% silica (SiO₂) plusNa₂O, CaO, and several minor additives. However, any material havingsuitable optical, electrical, thermal, and mechanical properties may beused as substrate 1228. Such substrates also can include, for example,other glass materials, plastics and thermoplastics (e.g., poly(methylmethacrylate), polystyrene, polycarbonate, allyl diglycol carbonate, SAN(styrene acrylonitrile copolymer), poly(4-methyl-1-pentene), polyester,polyamide), or mirror materials. If the substrate is formed from, forexample, glass, then substrate 1228 can be strengthened, e.g., bytempering, heating, or chemically strengthening. In otherimplementations, the substrate 1228 is not further strengthened, e.g.,the substrate is untempered.

In some embodiments, substrate 1228 is a glass pane sized forresidential or commercial window applications. The size of such a glasspane can vary widely depending on the specific needs of the residence orcommercial enterprise. In some embodiments, substrate 1228 can be formedof architectural glass. Architectural glass is typically used incommercial buildings, but also can be used in residential buildings, andtypically, though not necessarily, separates an indoor environment froman outdoor environment. In certain embodiments, a suitable architecturalglass substrate can be at least approximately 20 inches by approximately20 inches, and can be much larger, for example, approximately 80 inchesby approximately 120 inches, or larger. Architectural glass is typicallyat least about 2 millimeters (mm) thick and may be as thick as 6 mm ormore. Of course, electrochromic devices 1220 can be scalable tosubstrates 1228 smaller or larger than architectural glass, including inany or all of the respective length, width, or thickness dimensions. Insome embodiments, substrate 1228 has a thickness in the range ofapproximately 1 mm to approximately 10 mm. In some embodiments,substrate 1228 may be very thin and flexible, such as Gorilla Glass® orWillow™ Glass, each commercially available from Corning, Inc. ofCorning, N.Y., these glasses may be less than 1 mm thick, as thin as 0.3mm thick.

Electrochromic device 1220 is disposed over, for example, the innersurface 1222 of substrate 1228 of the outer pane 1216 (the pane adjacentthe outside environment). In some other embodiments, such as in coolerclimates or applications in which the IGUs 1202 receive greater amountsof direct sunlight (e.g., perpendicular to the surface of electrochromicdevice 1220), it may be advantageous for electrochromic device 1220 tobe disposed over, for example, the inner surface (the surface borderingthe volume 1226) of the inner pane adjacent the interior environment. Insome embodiments, electrochromic device 1220 includes a first conductivelayer (CL) 1230 (often transparent), a cathodically coloring layer 1232,often referred to as an electrochromic layer (EC) 1232, an ionconducting layer (IC) 1234, an anodically coloring layer 1236, oftenreferred to as a counter electrode layer (CE) 1236, and a secondconductive layer (CL) 1238 (often transparent). Again, layers 1230,1232, 1234, 1236, and 1238 are also collectively referred to aselectrochromic stack 1220.

A power source 1240 operable to apply an electric potential (V_(app)) tothe device and produce V_(eff) across a thickness of electrochromicstack 1220 and drive the transition of the electrochromic device 1220from, for example, a clear or lighter state (e.g., a transparent,semitransparent, or translucent state) to a tinted or darker state(e.g., a tinted, less transparent or less translucent state). In someother embodiments, the order of layers 1230, 1232, 1234, 1236, and 1238can be reversed or otherwise reordered or rearranged with respect tosubstrate 1228.

In some embodiments, one or both of first conductive layer 1230 andsecond conductive layer 1238 is formed from an inorganic and solidmaterial. For example, first conductive layer 1230, as well as secondconductive layer 1238, can be made from a number of different materials,including conductive oxides, thin metallic coatings, conductive metalnitrides, and composite conductors, among other suitable materials. Insome embodiments, conductive layers 1230 and 1238 are substantiallytransparent at least in the range of wavelengths where electrochromismis exhibited by the electrochromic layer 1232. Transparent conductiveoxides include metal oxides and metal oxides doped with one or moremetals. For example, metal oxides and doped metal oxides suitable foruse as first or second conductive layers 1230 and 1238 can includeindium oxide, indium tin oxide (ITO), doped indium oxide, tin oxide,doped tin oxide, zinc oxide, aluminum zinc oxide, doped zinc oxide,ruthenium oxide, doped ruthenium oxide, among others. As indicatedabove, first and second conductive layers 230 and 238 are sometimesreferred to as “transparent conductive oxide” (TCO) layers.

In some embodiments, commercially available substrates, such as glasssubstrates, already contain a transparent conductive layer coating whenpurchased. In some embodiments, such a product can be used for bothsubstrate 1238 and conductive layer 1230 collectively. Examples of suchglass substrates include conductive layer-coated glasses sold under thetrademark TEC Glass™ by Pilkington, of Toledo, Ohio and SUNGATE™ 300 andSUNGATE™ 500 by PPG Industries of Pittsburgh, Pa. Specifically, TECGlass™ is, for example, a glass coated with a fluorinated tin oxideconductive layer.

In some embodiments, first or second conductive layers 1230 and 1238 caneach be deposited by physical vapor deposition processes including, forexample, sputtering. In some embodiments, first and second conductivelayers 1230 and 1238 can each have a thickness in the range ofapproximately 0.01 μm to approximately 1 μm. In some embodiments, it maybe generally desirable for the thicknesses of the first and secondconductive layers 1230 and 1238 as well as the thicknesses of any or allof the other layers described below to be individually uniform withrespect to the given layer; that is, that the thickness of a given layeris uniform and the surfaces of the layer are smooth and substantiallyfree of defects or other ion traps.

A primary function of the first and second conductive layers 1230 and1238 is to spread an electric potential provided by a power source 1240,such as a voltage or current source, over surfaces of the electrochromicstack 1220 from outer surface regions of the stack to inner surfaceregions of the stack. As mentioned, the voltage applied to theelectrochromic device experiences some Ohmic potential drop from theouter regions to the inner regions as a result of a sheet resistance ofthe first and second conductive layers 1230 and 1238. In the depictedembodiment, bus bars 1242 and 1244 are provided with bus bar 1242 incontact with conductive layer 1230 and bus bar 1244 in contact withconductive layer 1238 to provide electric connection between the voltageor current source 1240 and the conductive layers 1230 and 1238. Forexample, bus bar 1242 can be electrically coupled with a first (e.g.,positive) terminal 1246 of power source 1240 while bus bar 1244 can beelectrically coupled with a second (e.g., negative) terminal 1248 ofpower source 1240.

In some embodiments, IGU 1202 includes a plug-in component 1250. In someembodiments, plug-in component 1250 includes a first electrical input1252 (e.g., a pin, socket, or other electrical connector or conductor)that is electrically coupled with power source terminal 1246 via, forexample, one or more wires or other electrical connections, components,or devices. Similarly, plug-in component 1250 can include a secondelectrical input 1254 that is electrically coupled with power sourceterminal 1248 via, for example, one or more wires or other electricalconnections, components, or devices. In some embodiments, firstelectrical input 1252 can be electrically coupled with bus bar 1242, andfrom there with first conductive layer 1230, while second electricalinput 1254 can be coupled with bus bar 1244, and from there with secondconductive layer 1238. The conductive layers 1230 and 1238 also can beconnected to power source 1240 with other conventional means as well asaccording to other means described below with respect to a windowcontroller. For example, as described below with reference to FIG. 13,first electrical input 1252 can be connected to a first power line whilesecond electrical input 1254 can be connected to a second power line.Additionally, in some embodiments, third electrical input 1256 can becoupled to a device, system, or building ground. Furthermore, in someembodiments, fourth and fifth electrical inputs/outputs 1258 and 1260,respectively, can be used for communication between, for example, awindow controller or microcontroller and a network controller.

In some embodiments, electrical input 1252 and electrical input 1254receive, carry, or transmit complementary power signals. In someembodiments, electrical input 1252 and its complement electrical input1254 can be directly connected to the bus bars 1242 and 1244,respectively, and on the other side, to an external power source thatprovides a variable DC voltage (e.g., sign and magnitude). The externalpower source can be a window controller (see element 1314 of FIG. 13)itself, or power from a building transmitted to a window controller orotherwise coupled to electrical inputs 1252 and 1254. In such anembodiment, the electrical signals transmitted through electricalinputs/outputs 1258 and 1260 can be directly connected to a memorydevice to allow communication between the window controller and thememory device. Furthermore, in such an embodiment, the electrical signalinput to electrical input 1256 can be internally connected or coupled(within IGU 1202) to either electrical input 1252 or 1254 or to the busbars 1242 or 1244 in such a way as to enable the electrical potential ofone or more of those elements to be remotely measured (sensed). This canallow the window controller to compensate for a voltage drop on theconnecting wires from the window controller to the electrochromic device1220.

In some embodiments, the window controller can be immediately attached(e.g., external to the IGU 1202 but inseparable by the user) orintegrated within the IGU 1202. For example, U.S. Pat. No. 8,213,074,incorporated by reference above, describes in detail various embodimentsof an “onboard” controller. In such an embodiment, electrical input 1252can be connected to the positive output of an external DC power source.Similarly, electrical input 1254 can be connected to the negative outputof the DC power source. As described below, however, electrical inputs1252 and 1254 can, alternately, be connected to the outputs of anexternal low voltage AC power source (e.g., a typical 24 V ACtransformer common to the HVAC industry). In such an embodiment,electrical inputs/outputs 1258 and 1260 can be connected to thecommunication bus between the window controller and a networkcontroller. In this embodiment, electrical input/output 1256 can beeventually (e.g., at the power source) connected with the earth ground(e.g., Protective Earth, or PE in Europe) terminal of the system.

Although the applied voltages may be provided as DC voltages, in someembodiments, the voltages actually supplied by the external power sourceare AC voltage signals. In some other embodiments, the supplied voltagesignals are converted to pulse-width modulated voltage signals. However,the voltages actually “seen” or applied to the bus bars 1242 and 1244are effectively DC voltages. Typically, the voltage oscillations appliedat terminals 1246 and 1248 are in the range of approximately 1 Hz to 1MHz, and in particular embodiments, approximately 100 kHz. In variousembodiments, the oscillations have asymmetric residence times for thedarkening (e.g., tinting) and lightening (e.g., clearing) portions of aperiod. For example, in some embodiments, transitioning from a firstless transparent state to a second more transparent state requires moretime than the reverse; that is, transitioning from the more transparentsecond state to the less transparent first state. As will be describedbelow, a controller can be designed or configured to apply a drivingvoltage meeting these requirements.

The oscillatory applied voltage control allows the electrochromic device1220 to operate in, and transition to and from, one or more stateswithout any necessary modification to the electrochromic device stack1220 or to the transitioning time. Rather, the window controller can beconfigured or designed to provide an oscillating drive voltage ofappropriate wave profile, taking into account such factors as frequency,duty cycle, mean voltage, amplitude, among other possible suitable orappropriate factors. Additionally, such a level of control permits thetransitioning to any state over the full range of optical states betweenthe two end states. For example, an appropriately configured controllercan provide a continuous range of transmissivity (% T) which can betuned to any value between end states (e.g., opaque and clear endstates).

To drive the device to an intermediate state using the oscillatorydriving voltage, a controller could simply apply the appropriateintermediate voltage. However, there can be more efficient ways to reachthe intermediate optical state. This is partly because high drivingvoltages can be applied to reach the end states but are traditionallynot applied to reach an intermediate state. One technique for increasingthe rate at which the electrochromic device 1220 reaches a desiredintermediate state is to first apply a high voltage pulse suitable forfull transition (to an end state) and then back off to the voltage ofthe oscillating intermediate state (just described). Stated another way,an initial low frequency single pulse (low in comparison to thefrequency employed to maintain the intermediate state) of magnitude andduration chosen for the intended final state can be employed to speedthe transition. After this initial pulse, a higher frequency voltageoscillation can be employed to sustain the intermediate state for aslong as desired.

In some embodiments, each IGU 1202 includes a component 1250 that is“pluggable” or readily-removable from IGU 1202 (e.g., for ease ofmaintenance, manufacture, or replacement). In some particularembodiments, each plug-in component 1250 itself includes a windowcontroller. That is, in some such embodiments, each electrochromicdevice 1220 is controlled by its own respective local window controllerlocated within plug-in component 1250. In some other embodiments, thewindow controller is integrated with another portion of frame 1218,between the glass panes in the secondary seal area, or within volume1226. In some other embodiments, the window controller can be locatedexternal to IGU 1202. In various embodiments, each window controller cancommunicate with the IGUs 1202 it controls and drives, as well ascommunicate to other window controllers, the network controller, BMS, orother servers, systems, or devices (e.g., sensors), via one or morewired (e.g., Ethernet) networks or wireless (e.g., WiFi) networks, forexample, via wired (e.g., Ethernet) interface 1263 or wireless (WiFi)interface 1265. See FIG. 13. Embodiments having Ethernet or Wificapabilities are also well-suited for use in residential homes and othersmaller-scale non-commercial applications. Additionally, thecommunication can be direct or indirect, e.g., via an intermediate nodebetween a master controller such as network controller 1312 and the IGU1202.

FIG. 13 depicts a window controller 1314, which may be deployed as, forexample, component 1250. In some embodiments, window controller 1314communicates with a network controller over a communication bus 1262.For example, communication bus 1262 can be designed according to theController Area Network (CAN) vehicle bus standard. In such embodiments,first electrical input 1252 can be connected to a first power line 1264while second electrical input 1254 can be connected to a second powerline 1266. In some embodiments, as described above, the power signalssent over power lines 1264 and 1266 are complementary; that is,collectively they represent a differential signal (e.g., a differentialvoltage signal). In some embodiments, line 1268 is coupled to a systemor building ground (e.g., an Earth Ground). In such embodiments,communication over CAN bus 1262 (e.g., between microcontroller 1274 andnetwork controller 1312) may proceed along first and secondcommunication lines 1270 and 1272 transmitted through electricalinputs/outputs 1258 and 1260, respectively, according to the CANopencommunication protocol or other suitable open, proprietary, or overlyingcommunication protocol. In some embodiments, the communication signalssent over communication lines 1270 and 1272 are complementary; that is,collectively they represent a differential signal (e.g., a differentialvoltage signal).

In some embodiments, component 1250 couples CAN communication bus 1262into window controller 1314, and in particular embodiments, intomicrocontroller 1274. In some such embodiments, microcontroller 1274 isalso configured to implement the CANopen communication protocol.Microcontroller 1274 is also designed or configured (e.g., programmed)to implement one or more drive control algorithms in conjunction withpulse-width modulated amplifier or pulse-width modulator (PWM) 1276,smart logic 1278, and signal conditioner 1280. In some embodiments,microcontroller 1274 is configured to generate a command signalV_(COMMAND), e.g., in the form of a voltage signal, that is thentransmitted to PWM 1276. PWM 1276, in turn, generates a pulse-widthmodulated power signal, including first (e.g., positive) componentV_(PW1) and second (e.g., negative) component V_(PW2), based onV_(COMMAND). Power signals V_(PW1) and V_(PW2) are then transmittedover, for example, interface 1288, to IGU 1202, or more particularly, tobus bars 1242 and 1244 in order to cause the desired optical transitionsin electrochromic device 1220. In some embodiments, PWM 1276 isconfigured to modify the duty cycle of the pulse-width modulated signalssuch that the durations of the pulses in signals V_(PW1) and V_(PW2) arenot equal: for example, PWM 1276 pulses V_(PW1) with a first 60% dutycycle and pulses V_(PW2) for a second 40% duty cycle. The duration ofthe first duty cycle and the duration of the second duty cyclecollectively represent the duration, t_(PWM) of each power cycle. Insome embodiments, PWM 1276 can additionally or alternatively modify themagnitudes of the signal pulses V_(PW1) and V_(PW2).

In some embodiments, microcontroller 1274 is configured to generateV_(COMMAND) based on one or more factors or signals such as, forexample, any of the signals received over CAN bus 1262 as well asvoltage or current feedback signals, V_(FB) and I_(FB) respectively,generated by PWM 1276. In some embodiments, microcontroller 1274determines current or voltage levels in the electrochromic device 1220based on feedback signals I_(FB) or V_(FB), respectively, and adjustsV_(COMMAND) according to one or more rules or algorithms described aboveto effect a change in the relative pulse durations (e.g., the relativedurations of the first and second duty cycles) or amplitudes of powersignals V_(PW1) and V_(PW2) to produce voltage profiles as describedabove. Additionally or alternatively, microcontroller 1274 can alsoadjust V_(COMMAND) in response to signals received from smart logic 1278or signal conditioner 1280. For example, a conditioning signal V_(CON)can be generated by signal conditioner 1280 in response to feedback fromone or more networked or non-networked devices or sensors, such as, forexample, an exterior photosensor or photodetector 1282, an interiorphotosensor or photodetector 1284, a thermal or temperature sensor 1286,or a tint command signal V_(TC). For example, additional embodiments ofsignal conditioner 1280 and V_(CON) are also described in U.S. Pat. No.8,705,162, which is herein incorporated by reference.

In certain embodiments, V_(TC) can be an analog voltage signal between 0V and 10 V that can be used or adjusted by users (such as residents orworkers) to dynamically adjust the tint of an IGU 1202 (for example, auser can use a control in a room or zone of building similarly to athermostat to finely adjust or modify a tint of the IGUs 1202 in theroom or zone) thereby introducing a dynamic user input into the logicwithin microcontroller 1274 that determines V_(COMMAND). For example,when set in the 0 to 2.5 V range, V_(TC) can be used to cause atransition to a 5% T state, while when set in the 2.51 to 5 V range,V_(TC) can be used to cause a transition to a 20% T state, and similarlyfor other ranges such as 5.1 to 7.5 V and 7.51 to 10 V, among otherrange and voltage examples. In some embodiments, signal conditioner 1280receives the aforementioned signals or other signals over acommunication bus or interface 1290. In some embodiments, PWM 1276 alsogenerates V_(COMMAND) based on a signal V_(SMART) received from smartlogic 1278. In some embodiments, smart logic 1278 transmits V_(SMART)over a communication bus such as, for example, an Inter-IntegratedCircuit (I²C) multi-master serial single-ended computer bus. In someother embodiments, smart logic 1278 communicates with memory device 1292over a 1-WIRE device communications bus system protocol (by DallasSemiconductor Corp., of Dallas, Tex.).

In some embodiments, microcontroller 1274 includes a processor, chip,card, or board, or a combination of these, which includes logic forperforming one or more control functions. Power and communicationfunctions of microcontroller 1274 may be combined in a single chip, forexample, a programmable logic device (PLD) chip or field programmablegate array (FPGA), or similar logic. Such integrated circuits cancombine logic, control and power functions in a single programmablechip. In one embodiment, where one pane 1216 has two electrochromicdevices 1220 (e.g., on opposite surfaces) or where IGU 1202 includes twoor more panes 1216 that each include an electrochromic device 1220, thelogic can be configured to control each of the two electrochromicdevices 1220 independently from the other. However, in one embodiment,the function of each of the two electrochromic devices 1220 iscontrolled in a synergistic fashion, for example, such that each deviceis controlled in order to complement the other. For example, the desiredlevel of light transmission, thermal insulative effect, or otherproperty can be controlled via a combination of states for each of theindividual electrochromic devices 1220. For example, one electrochromicdevice may be placed in a tinted state while the other is used forresistive heating, for example, via a transparent electrode of thedevice. In another example, the optical states of the two electrochromicdevices are controlled so that the combined transmissivity is a desiredoutcome.

In general, the logic used to control electrochromic device transitionscan be designed or configured in hardware and/or software. In otherwords, the instructions for controlling the drive circuitry may be hardcoded or provided as software. It may be said that the instructions areprovided by “programming.” Such programming is understood to includelogic of any form including hard coded logic in digital signalprocessors and other devices which have specific algorithms implementedas hardware. Programming is also understood to include software orfirmware instructions that may be executed on a general purposeprocessor. In some embodiments, instructions for controlling applicationof voltage to the bus bars are stored on a memory device associated withthe controller or are provided over a network. Examples of suitablememory devices include semiconductor memory, magnetic memory, opticalmemory, and the like. The computer program code for controlling theapplied voltage can be written in any conventional computer readableprogramming language such as assembly language, C, C++, Pascal, Fortran,and the like. Compiled object code or script is executed by theprocessor to perform the tasks identified in the program.

As described above, in some embodiments, microcontroller 1274, or windowcontroller 1314 generally, also can have wireless capabilities, such aswireless control and powering capabilities. For example, wirelesscontrol signals, such as radio-frequency (RF) signals or infra-red (IR)signals can be used, as well as wireless communication protocols such asWiFi (mentioned above), Bluetooth, Zigbee, EnOcean, among others, tosend instructions to the microcontroller 1274 and for microcontroller1274 to send data out to, for example, other window controllers, anetwork controller 1312, or directly to a BMS 1310. In variousembodiments, wireless communication can be used for at least one ofprogramming or operating the electrochromic device 1220, collecting dataor receiving input from the electrochromic device 1220 or the IGU 1202generally, collecting data or receiving input from sensors, as well asusing the window controller 1314 as a relay point for other wirelesscommunications. Data collected from IGU 1202 also can include countdata, such as a number of times an electrochromic device 1220 has beenactivated (cycled), an efficiency of the electrochromic device 1220 overtime, among other useful data or performance metrics.

The window controller 1314 also can have wireless power capability. Forexample, window controller can have one or more wireless power receiversthat receive transmissions from one or more wireless power transmittersas well as one or more wireless power transmitters that transmit powertransmissions enabling window controller 1314 to receive powerwirelessly and to distribute power wirelessly to electrochromic device1220. Wireless power transmission includes, for example, induction,resonance induction, RF power transfer, microwave power transfer, andlaser power transfer. For example, U.S. patent application Ser. No.12/971,576 naming Rozbicki as inventor, titled “WIRELESS POWEREDELECTROCHROMIC WINDOWS,” and filed 17 Dec. 2010, incorporated byreference above, describes in detail various embodiments of wirelesspower capabilities.

In order to achieve a desired optical transition, the pulse-widthmodulated power signal is generated such that the positive componentV_(PW1) is supplied to, for example, bus bar 1244 during the firstportion of the power cycle, while the negative component V_(PW2) issupplied to, for example, bus bar 1242 during the second portion of thepower cycle.

In some cases, depending on the frequency (or inversely the duration) ofthe pulse-width modulated signals, this can result in bus bar 1244floating at substantially the fraction of the magnitude of V_(PW1) thatis given by the ratio of the duration of the first duty cycle to thetotal duration t_(PWM) of the power cycle. Similarly, this can result inbus bar 1242 floating at substantially the fraction of the magnitude ofV_(PW2) that is given by the ratio of the duration of the second dutycycle to the total duration t_(PWM) of the power cycle. In this way, insome embodiments, the difference between the magnitudes of thepulse-width modulated signal components V_(PW1) and V_(PW2) is twice theeffective DC voltage across terminals 1246 and 1248, and consequently,across electrochromic device 1220. Said another way, in someembodiments, the difference between the fraction (determined by therelative duration of the first duty cycle) of V_(PW1) applied to bus bar1244 and the fraction (determined by the relative duration of the secondduty cycle) of V_(PW2) applied to bus bar 1242 is the effective DCvoltage V_(EFF) applied to electrochromic device 1220. The current IEFFthrough the load—electromagnetic device 1220—is roughly equal to theeffective voltage VEFF divided by the effective resistance or impedanceof the load.

Those of ordinary skill in the art will also understand that thisdescription is applicable to various types of drive mechanism includingfixed voltage (fixed DC), fixed polarity (time varying DC) or areversing polarity (AC, MF, RF power etc. with a DC bias).

The controller may be configured to monitor voltage and/or current fromthe optically switchable device. In some embodiments, the controller isconfigured to calculate current by measuring voltage across a knownresistor in the driving circuit. Other modes of measuring or calculatingcurrent may be employed. These modes may be digital or analog.

Electrochromic Devices

For context, examples of electrochromic device designs now will bedescribed. FIG. 14 schematically depicts an electrochromic device 1400in cross-section. Electrochromic device 1400 includes a substrate 1402,a first conductive layer (CL) 1404, a cathodically coloringelectrochromic layer (EC) 1406, an ion conducting layer (IC) 1408, ananodically coloring counter electrode layer (CE) 1410, and a secondconductive layer (CL), 1414. Layers 1404, 1406, 1408, 1410, and 1414 arecollectively referred to as an electrochromic stack 1420. A voltagesource 1416 operable to apply an electric potential acrosselectrochromic stack 1420 effects the transition of the electrochromicdevice from, for example, a clear state to a tinted state (depicted).The order of layers can be reversed with respect to the substrate.

Electrochromic devices having distinct layers as described can befabricated as all solid state and/or all inorganic devices with lowdefectivity. Such devices and methods of fabricating them are describedin more detail in U.S. patent application Ser. No. 12/645,111, entitled,“Fabrication of Low-Defectivity Electrochromic Devices,” filed on Dec.22, 2009 and naming Mark Kozlowski et al. as inventors, and in U.S. Pat.No. 8,432,603, entitled, “Electrochromic Devices,” filed on Dec. 22,2009 and naming Zhongchun Wang et al. as inventors, both of which areincorporated by reference herein for all purposes. It should beunderstood, however, that any one or more of the layers in the stack maycontain some amount of organic material. The same can be said forliquids that may be present in one or more layers in small amounts. Itshould also be understood that solid state material may be deposited orotherwise formed by processes employing liquid components such ascertain processes employing sol-gels or chemical vapor deposition.

In embodiments described herein, the electrochromic device reversiblycycles between a clear state and a tinted state. In some cases, when thedevice is in a clear state, a potential is applied to the electrochromicstack 1420 such that available ions in the stack reside primarily in thecounter electrode 1410. When the potential on the electrochromic stackis reversed, the ions are transported across the ion conducting layer1408 to the electrochromic material 1406 and cause the material totransition to the tinted state.

Referring again to FIG. 14, voltage source 1416 may be configured tooperate in conjunction with radiant and other environmental sensors. Asdescribed herein, voltage source 1416 interfaces with a devicecontroller (not shown in this figure). Additionally, voltage source 1416may interface with an energy management system that controls theelectrochromic device according to various criteria such as the time ofyear, time of day, and measured environmental conditions. Such an energymanagement system, in conjunction with large area electrochromic devices(e.g., an electrochromic window), can dramatically lower the energyconsumption of a building.

Any material having suitable optical, electrical, thermal, andmechanical properties may be used as substrate 1402. Such substratesinclude, for example, glass, plastic, and mirror materials. Suitableglasses include either clear or tinted soda lime glass, including sodalime float glass. The glass may be tempered or untempered.

In many cases, the substrate is a glass pane sized for residentialwindow applications. The size of such glass pane can vary widelydepending on the specific needs of the residence. In other cases, thesubstrate is architectural glass. Architectural glass is typically usedin commercial buildings, but may also be used in residential buildings,and typically, though not necessarily, separates an indoor environmentfrom an outdoor environment. In certain embodiments, architectural glassis at least 20 inches by 20 inches, and can be much larger, for example,as large as about 80 inches by 120 inches. Architectural glass istypically at least about 2 mm thick. Of course, electrochromic devicesare scalable to substrates smaller or larger than architectural glass.Further, the electrochromic device may be provided on a mirror of anysize and shape.

On top of substrate 1402 is conductive layer 1404. In certainembodiments, one or both of the conductive layers 1404 and 1414 isinorganic and/or solid. Conductive layers 1404 and 1414 may be made froma number of different materials, including conductive oxides, thinmetallic coatings, conductive metal nitrides, and composite conductors.Typically, conductive layers 1404 and 1414 are transparent at least inthe range of wavelengths where electrochromism is exhibited by theelectrochromic layer. Transparent conductive oxides include metal oxidesand metal oxides doped with one or more metals. Examples of such metaloxides and doped metal oxides include indium oxide, indium tin oxide,doped indium oxide, tin oxide, doped tin oxide, zinc oxide, aluminumzinc oxide, doped zinc oxide, ruthenium oxide, doped ruthenium oxide andthe like. Since oxides are often used for these layers, they aresometimes referred to as “transparent conductive oxide” (TCO) layers.Thin metallic coatings that are substantially transparent may also beused.

The function of the conductive layers is to spread an electric potentialprovided by voltage source 1416 over surfaces of the electrochromicstack 1420 to interior regions of the stack, with relatively littleohmic potential drop. The electric potential is transferred to theconductive layers though electrical connections to the conductivelayers. In some embodiments, bus bars, one in contact with conductivelayer 1404 and one in contact with conductive layer 1414, provide theelectric connection between the voltage source 1416 and the conductivelayers 1404 and 1414. The conductive layers 1404 and 1414 may also beconnected to the voltage source 1416 with other conventional means.

Overlaying conductive layer 1404 is electrochromic layer 1406. In someembodiments, electrochromic layer 1406 is inorganic and/or solid. Thecathodically coloring electrochromic layer may contain any one or moreof a number of different cathodically coloring electrochromic materials,including metal oxides. Such metal oxides include tungsten oxide (WO₃),molybdenum oxide (MoO₃), niobium oxide (Nb₂O₅), titanium oxide (TiO₂),copper oxide (CuO), iridium oxide (Ir₂O₃), chromium oxide (Cr₂O₃),manganese oxide (Mn₂O₃), vanadium oxide (V₂O₅), nickel oxide (Ni₂O₃),cobalt oxide (Co₂O₃) and the like. During operation, cathodicallycoloring electrochromic layer 1406 transfers ions to and receives ionsfrom anodically coloring counter electrode layer 1410 to cause opticaltransitions.

Generally, the tinting (or change in any optical property—for example,absorbance, reflectance, and transmittance) of the electrochromicmaterial is caused by reversible ion insertion into the material (forexample, intercalation) and a corresponding injection of a chargebalancing electron. Typically some fraction of the ions responsible forthe optical transition is irreversibly bound up in the electrochromicmaterial. Some or all of the irreversibly bound ions are used tocompensate “blind charge” in the material. In most electrochromicmaterials, suitable ions include lithium ions (Li⁺) and hydrogen ions(H⁺) (that is, protons). In some cases, however, other ions will besuitable. In various embodiments, lithium ions are used to produce theelectrochromic phenomena. Intercalation of lithium ions into tungstenoxide (WO_(3-y) (0<y≤˜0.3)) causes the tungsten oxide to change fromtransparent (clear state) to blue (tinted state).

Referring again to FIG. 14, in electrochromic stack 1420, ion conductinglayer 1408 is sandwiched between electrochromic layer 1406 and counterelectrode layer 1410. In some embodiments, counter electrode layer 1410is inorganic and/or solid. The counter electrode layer may comprise oneor more of a number of different materials that serve as a reservoir ofions when the electrochromic device is in the clear state. During anelectrochromic transition initiated by, for example, application of anappropriate electric potential, the anodically coloring counterelectrode layer transfers some or all of the ions it holds to thecathodically coloring electrochromic layer, changing the electrochromiclayer to the tinted state. Concurrently, in the case of NiWO, theanodically coloring counter electrode layer tints with the loss of ions.

In some embodiments, suitable anodically coloring materials for thecounter electrode complementary to WO₃ include nickel oxide (NiO),nickel tungsten oxide (NiWO), nickel vanadium oxide, nickel chromiumoxide, nickel aluminum oxide, nickel manganese oxide, nickel magnesiumoxide, chromium oxide (Cr₂O₃), manganese oxide (MnO₂), Prussian blue.Other suitable anodically coloring materials are further discussed inthe following U.S. patent applications, each of which is incorporated byreference in its entirety: U.S. Provisional Patent Application No.61/998,111, filed May 2, 2014, naming Pradhan, et. al. as inventors, andU.S. Provisional Patent Application No. 61/988,107, filed May 2, 2014,and naming Gillaspie, et. al. as inventors.

When charge is removed from a counter electrode 1410 made of nickeltungsten oxide (that is, ions are transported from the counter electrode1410 to the electrochromic layer 1406), the counter electrode layer willtransition from a transparent state to a tinted state.

In the depicted electrochromic device, between electrochromic layer 1406and counter electrode layer 1410, there is the ion conducting layer1408. Ion conducting layer 1408 serves as a medium through which ionsare transported (in the manner of an electrolyte) when theelectrochromic device transitions between the clear state and the tintedstate. Preferably, ion conducting layer 1408 is highly conductive to therelevant ions for the electrochromic and the counter electrode layers,but has sufficiently low electron conductivity that negligible electrontransfer takes place during normal operation. A thin ion conductinglayer with high ionic conductivity permits fast ion conduction and hencefast switching for high performance electrochromic devices. In certainembodiments, the ion conducting layer 1408 is inorganic and/or solid. Inother embodiments, the ion conducting layer 1408 is omitted.

Examples of suitable ion conducting layers (for electrochromic deviceshaving a distinct IC layer) include silicates, silicon oxides, tungstenoxides, tantalum oxides, niobium oxides, and borates. The silicon oxidesinclude silicon-aluminum-oxide. These materials may be doped withdifferent dopants, including lithium. Lithium doped silicon oxidesinclude lithium silicon-aluminum-oxide. In some embodiments, the ionconducting layer comprises a silicate-based structure. In someembodiments, a silicon-aluminum-oxide (SiAlO) is used for the ionconducting layer 1408.

The electrochromic device 1400 may include one or more additional layers(not shown) such as one or more passive layers. Passive layers used toimprove certain optical properties may be included in electrochromicdevice 1400. Passive layers for providing moisture or scratch resistancemay also be included in the electrochromic device 1400. For example, theconductive layers may be treated with anti-reflective or protectiveoxide or nitride layers. Other passive layers may serve to hermeticallyseal the electrochromic device 1400.

FIG. 15 is a schematic cross-section of an electrochromic device in aclear state (or transitioning to a clear state). In accordance withspecific embodiments, an electrochromic device 1500 includes a tungstenoxide cathodically coloring electrochromic layer (EC) 1506 and anickel-tungsten oxide anodically coloring counter electrode layer (CE)1510. The electrochromic device 1500 also includes a substrate 1502,conductive layer (CL) 1504, ion conducting layer (IC) 1508, andconductive layer (CL) 1514.

A power source 1516 is configured to apply a potential and/or current toelectrochromic stack 1520 through suitable connections (for example, busbars) to conductive layers 1504 and 1514. In some embodiments, thevoltage source is configured to apply a potential of about 2 V in orderto drive a transition of the device from one optical state to another.The polarity of the potential as shown in FIG. 15 is such that the ions(lithium ions in this example) primarily reside (as indicated by thedashed arrow) in nickel-tungsten oxide anodically coloring counterelectrode layer 1510.

FIG. 16 is a schematic cross-section of electrochromic device 1500 shownin FIG. 15 but in a tinted state (or transitioning to a tinted state).In FIG. 17, the polarity of voltage source 1516 is reversed, so that theelectrochromic layer is made more negative to accept additional lithiumions, and thereby transition to the tinted state. As indicated by thedashed arrow, lithium ions are transported across the ion conductinglayer 1508 to the tungsten oxide electrochromic layer 1506. The tungstenoxide electrochromic layer 1506 is shown in the tinted state. Thenickel-tungsten oxide counter electrode 1510 is also shown in the tintedstate. As explained, nickel-tungsten oxide becomes progressively moreopaque as it gives up (deintercalates) lithium ions. In this example,there is a synergistic effect where the transition to tinted states forboth layers 1506 and 1510 are additive toward reducing the amount oflight transmitted through the stack and substrate.

As described above, an electrochromic device may include a cathodicallycoloring layer, often referred to as an electrochromic (EC) electrodelayer (or more simply as an electrochromic layer) and an anodicallycoloring counter electrode layer, often referred to as a counterelectrode (CE) layer, separated by an ionically conductive (IC) layerthat is highly conductive to ions and highly resistive to electrons. Asconventionally understood, the ionically conductive layer preventsshorting between the electrochromic layer and the counter electrodelayer. The ionically conductive layer allows the electrochromic andcounter electrodes to hold a charge and thereby maintain their clear ortinted states. In electrochromic devices having distinct layers, thecomponents form a stack which includes the ion conducting layersandwiched between the electrochromic electrode layer and the counterelectrode layer. The boundaries between these three stack components aredefined by abrupt changes in composition and/or microstructure. Thus,the devices have three distinct layers with two abrupt interfaces.

In accordance with certain embodiments, the counter electrode andelectrochromic electrodes are formed immediately adjacent one another,sometimes in direct contact, without separately depositing an ionicallyconducting layer. In some embodiments, electrochromic devices having aninterfacial region rather than a distinct IC layer are employed withcontrollers described herein. Such devices, and methods of fabricatingthem, are described in U.S. Pat. Nos. 8,300,298, 8,582,193, 8,764,950,8,764,951, each of the four patents is entitled “ElectrochromicDevices,” each names Zhongchun Wang et al. as inventors, and each isincorporated by reference herein in its entirety.

FIG. 17 is a schematic cross-section of an electrochromic device 1700 ina tinted state, where the device has an interfacial region, 1708, whichdoes not contain a distinct IC layer. Voltage source 1716, conductivelayers 1714 and 1704, and substrate 1702 are essentially the same asdescribed in relation to FIGS. 14 and 15. Between conductive layers 1714and 1704 is a region 1710, which includes anodically coloring counterelectrode layer 1710, cathodically coloring electrochromic layer 1706and an interfacial region, 1708, between them, rather than a distinct IClayer. In this example, there is no distinct boundary between counterelectrode layer 1710 and interfacial region 1708, nor is there adistinct boundary between electrochromic layer 1706 and interfacialregion 1708. Rather, there is a diffuse transition between CE layer 1710and interfacial region 1708, and between interfacial region 1708 and EClayer 1706.

Although the foregoing invention has been described in some detail tofacilitate understanding, the described embodiments are to be consideredillustrative and not limiting. It will be apparent to one of ordinaryskill in the art that certain changes and modifications can be practicedwithin the scope of the appended claims.

What is claimed is:
 1. A controller comprising a microprocessor, thecontroller configured to control an optical transition of an opticallyswitchable device, by: (a) applying a voltage and/or a current fordriving a first optically switchable device to transition from astarting optical state to an ending optical state; (b) before thetransition is complete, determining an electrical characteristic of thefirst optically switchable device; and, responsive to the determinedelectrical characteristic: (c) ramping, over time, the applied voltageand/or the current at a ramp rate to a target voltage value; and (d)making an adjustment to the ramp rate, to maintain the determinedelectrical characteristic between threshold levels, wherein theadjustment comprises: (i) stopping the ramping, reversing the directionof the ramping, decreasing a slope of the ramp rate, or increasing theslope of the ramp rate; and (ii) substantially matching, during theoptical transition, a tint level of the first optically switchabledevice to that of a second optically switchable device proximate thefirst optically switchable device.
 2. The controller of claim 1, whereinthe first optically switchable device and/or the second opticallyswitchable device is an electrochromic (EC) window.
 3. The controller ofclaim 2, wherein the EC window is included in a folding curtain wallcomprising at least two EC windows coupled by ribbon connectors.
 4. Thecontroller of claim 1, wherein the determined electrical characteristiccomprises an open circuit voltage across two electrodes of the opticallyswitchable device.
 5. The controller of claim 1, wherein the determinedelectrical characteristic comprises a current flowing between twoelectrodes of the optically switchable device.
 6. The controller ofclaim 1, wherein the determined electrical characteristic comprises avoltage and/or a current, and wherein using the determined electricalcharacteristic comprises adjusting the applied voltage and/or currentused to drive the transition based at least in part on the determinedelectrical characteristic to ensure that the optically switchable deviceis maintained during the optical transition (i) within a safe operatingrange of current density and/or (ii) within a safe operating voltagerange, wherein the safe operating range of current density and the safeoperating voltage range facilitate operation such that the opticallyswitchable device is not degraded.
 7. The controller of claim 6, whereinthe safe operating range of current density has a maximum currentdensity magnitude between (I) about seventy (70) microamperes percentimeter square and (II) about two hundred and fifty (250)microamperes per centimeter square (μA/cm²).
 8. The controller of claim6, wherein the safe operating voltage range has a maximum magnitudebetween (I) about five (5) Volts and (II) about nine (9) Volts (V). 9.The controller of claim 1, wherein the determined electricalcharacteristic comprises a voltage and/or a current, and wherein usingthe determined electrical characteristic comprises adjusting the appliedvoltage and/or current used to drive the transition based at least inpart on the determined electrical characteristic to ensure that theoptical transition is occurring at a rate of optical transition that isat least as high as a target rate of optical transition.
 10. Thecontroller of claim 9, wherein using the determined electricalcharacteristic further comprises adjusting the applied voltage and/orcurrent based at least in part on the determined electricalcharacteristic to ensure that the optical transition occurs within atarget timeframe.
 11. The controller of claim 1, wherein the determinedelectrical characteristic comprises a voltage and/or a current, andwherein using the determined electrical characteristic comprisesadjusting the applied voltage and/or current used to drive thetransition based at least in part on the determined electricalcharacteristic to determine whether the optically switchable device isat or near the ending optical state.
 12. The controller of claim 11,wherein the determined electrical characteristic comprises a currentthat occurs in response to open circuit voltage conditions applied tothe optically switchable device.
 13. The controller of claim 12, thecontroller further configured to determine a quantity of chargedelivered to drive the optical transition, and, based at least in parton the determined quantity of charge delivered, determining whether theoptically switchable device is at or near the ending optical state. 14.The controller of claim 1, the controller further configured to receivea command to transition the optically switchable device to a thirdoptical state after initiation of the optical transition from thestarting optical state to the ending optical state, wherein the thirdoptical state is different from the ending optical state, and whereinusing the determined electrical characteristic comprises adjusting theapplied voltage and/or current used to drive the optical transition isbased at least in part on the determined electrical characteristic tothereby drive the optically switchable device to the third opticalstate.
 15. The controller of claim 1, wherein the target voltage valueis (i) a target drive voltage or (ii) a target hold voltage.
 16. Thecontroller of claim 1, wherein the determined electrical characteristiccomprises a conducted current, and the controller is further configuredto: ramp the applied voltage and/or current at an increased rate inresponse to a decrease in the conducted current.
 17. The controller ofclaim 1, wherein the determined electrical characteristic comprises aconducted current, and the controller is further configured to: ramp theapplied voltage and/or current at a decreased rate in response to anincrease in the conducted current.
 18. A controller comprising amicroprocessor, the controller configured to maintain substantiallymatching tint levels or tint rates in a plurality of electrochromic (EC)windows by: (a) probing the plurality of EC windows to determine anelectrical response for each window, each electrical response having amagnitude; (b) analyzing the magnitude of the determined electricalresponses for the plurality of EC windows; and (c) based on themagnitudes of the determined electrical responses, scaling a voltage orcurrent applied to one or more of the plurality of EC windows to therebymatch the tint levels or tint rates in each of the plurality of ECwindows.
 19. The controller of claim 18, wherein two or more of theplurality of EC window are included in a folding curtain wall.
 20. Thecontroller of claim 19, wherein adjacent ones of the plurality of ECwindows are coupled by ribbon connectors.
 21. A controller comprising amicroprocessor, the controller configured to transition a plurality ofelectrochromic (EC) windows at substantially matching tint rates by: (a)determining a transition time over which the plurality of EC windows areto be transitioned from a starting optical state to an ending opticalstate, wherein the transition time is based, at least in part, on aminimum time over which a slowest transitioning window in the pluralityof EC windows transitions from the starting optical state to the endingoptical state; and (b) applying one or more drive conditions to each ofthe windows in the plurality of EC windows, wherein the one or moredrive conditions applied to each window are sufficient to cause eachwindow to transition from the starting optical state to the endingoptical state within the transition time.
 22. The controller of claim21, wherein the controller, while applying the one or more driveconditions, is configured to: probe the plurality of EC windows todetermine an electrical response for each window, measure the electricalresponse for each window, determine whether the electrical response foreach window indicates that the window will reach the ending opticalstate within the transition time, and if it is determined that thewindow will reach the ending optical state within the transition time,continue to apply the driving conditions to reach the ending opticalstate, and if it is determined that the window will not reach the endingoptical state within the transition time, increase a voltage and/orcurrent applied to the window to thereby cause the window to reach theending optical state within the transition time.
 23. The controller ofclaim 22, wherein: if it is determined that the window will reach theending optical state substantially before the transition time, thecontroller is configured to decrease a drive voltage and/or currentapplied to the window to thereby cause the window to reach the endingoptical state at a time closer to the transition time than wouldotherwise occur without decreasing the drive voltage and/or current. 24.The controller of claim 21, wherein the transition time is based, atleast in part, on a size of a largest window in the plurality of ECwindows.
 25. The controller of claim 24, the controller furtherconfigured to define the plurality of EC windows to be transitionedbased on one or more criteria selected from the group consisting of:pre-defined zones of windows, instantaneously-defined zones of windows,window properties, and user preferences.
 26. The controller of claim 25,the controller further configured to define the plurality of EC windowsto be transitioned by determining a first plurality of EC windows anddetermining a second plurality of EC windows, wherein the transitiontime determined in (a) is a first transition time over which the firstplurality of EC windows are to be transitioned, and wherein thetransition time in (b) is the first transition time, the controllerfurther configured to: (c) after beginning to apply the one or moredrive conditions in (b) and before the first plurality of EC windowsreaches the ending optical state, determine a second transition timeover which the second plurality of EC windows are to be transitioned toa third optical state, wherein the third optical state may be thestarting optical state, the ending optical state, or a different opticalstate, wherein the second transition time is based, at least in part, ona minimum time over which a slowest transitioning window in the secondplurality of EC windows transitions to the third optical state, and (d)apply one or more drive conditions to each of the windows in the secondplurality of EC windows, wherein the one or more drive conditionsapplied to each window are sufficient to cause each window to transitionto the third optical state substantially within the second transitiontime.
 27. The controller of claim 21, wherein each window in theplurality of EC windows comprises a memory component comprising aspecified transition time for that window, and wherein (a) comprisescomparing the specified transition time for each window in the pluralityof EC windows to thereby determine which window is the slowesttransitioning window in the plurality of EC windows.
 28. The controllerof claim 21, wherein two or more of the plurality of EC window areincluded in a folding curtain wall.
 29. The controller of claim 28,wherein adjacent ones of the plurality of EC windows are coupled byribbon connectors.